Free OBD2 fault code lookup

Symptoms

• Passenger Airbag Off light stays illuminated with an adult occupant
• SRS warning light permanently visible on dash

Common causes

• Defective passenger seat weight sensor mat
• Spilled liquids on the front passenger seat shorting the OCS mat
• Out of calibration OCS module

What to do?

Check for physical damage or wetness on the passenger seat. Attempt an OCS system recalibration using an advanced diagnostic scanner. If recalibration fails or the sensor mat is physically failed, the lower seat cushion/sensor mat must be replaced.

Symptoms

• The dashboard seatbelt unfastened lamp stays dark when unbuckled
• The seatbelt warning light stays illuminated despite the seatbelt being securely clicked in

Common causes

• Failed LED/bulb inside the instrument cluster assembly
• Open or short circuit in the driver seatbelt indicator dashboard warning line

What to do?

Perform an instrument cluster self-test sweep using a scanner to see if the bulb illuminates. If the bulb works during the sweep, the issue lies in the feedback loop signal from the BCM or the driver buckle switch wiring.

Symptoms

• Airbag warning light illuminated on dashboard
• Airbag system completely disabled

Common causes

• Faulty airbag clock spring

Symptoms

• Airbag warning light illuminated on dashboard
• Airbag system completely disabled

Common causes

• Faulty airbag clock spring
• Loose or damaged wiring connectors under the steering column
• Corroded pins in the SRS harness
• Faulty driver-side airbag module

What to do?

Disconnect the battery for 15+ minutes to safely deactivate the SRS system. Inspect the clock spring for continuity and check all steering column wiring harnesses for open circuits. Replace the clock spring or faulty wiring.

Symptoms

• Airbag warning light illuminated on dashboard
• Airbag system completely disabled

Common causes

• Faulty airbag clock spring

Symptoms

• SRS airbag light illuminated on dashboard
• Passenger airbag indicator light malfunctioning

Common causes

• Faulty passenger airbag module
• Damaged wiring or connectors behind the dashboard/glovebox
• Blown SRS system fuse

What to do?

Safely disconnect the vehicle battery. Remove the glovebox or access panel to inspect the passenger airbag module connectors and wiring loom. Test for resistance and replace the faulty passenger airbag assembly or repair the wiring harness if damaged.

Symptoms

• Airbag light illuminated on the instrument cluster
• Side-impact protection system disabled

Common causes

• Damaged wiring harness underneath the driver or left-passenger seat
• Faulty left side-impact airbag module
• Corroded connector terminals due to floor moisture

What to do?

Check the yellow SRS wiring harness and connectors under the left-side seat. Frequently, moving the seat back and forth damages or loosens these wires. Clean the connectors with electronic cleaner, secure the connections, and clear the code.

Symptoms

• SRS warning light permanently illuminated
• Right-side curtain or seat airbag deactivated

Common causes

• Damaged or loose wiring under the right seat
• Corroded plug terminals or seat slider pinching the loom
• Defective right-side airbag module

What to do?

Inspect the yellow SRS loom underneath the front right seat. Ensure the harness is unpinched and firmly clipped. Clean the pins with contact cleaner, clear the DTC, and retest. If the issue remains, test module circuit resistance.

Symptoms

• Seatbelt warning chime rings even when belted
• Seatbelt warning light stays on or fails to light up

Common causes

• Faulty microswitch inside the driver's seatbelt buckle assembly
• Broken or severed wiring under the driver's seat
• Debris or liquid spilled inside the buckle mechanism

What to do?

Check for debris or foreign objects trapped inside the seatbelt latch and clean it out. Inspect the wiring underneath the seat for signs of wear or disconnection. If wiring is fine, replace the seatbelt buckle assembly which houses the integrated microswitch.

Symptoms

• SRS airbag warning light illuminated
• Pretensioner system disabled in an accident

Common causes

• Faulty seatbelt pretensioner squib circuit
• Loose or broken wiring connector at the base of the B-pillar or seat
• Corroded connector pins

What to do?

Inspect the wiring harness connecting to the seatbelt pretensioner mechanism (typically located at the base of the B-pillar or attached to the seat buckle). Check for loose connections or corrosion. Replace the pretensioner mechanism if internal resistance is out of spec.

Symptoms

• Airbag/SRS indicator light remains on
• Center seat restraint safety features disabled

Common causes

• Faulty center seatbelt load limiter assembly
• Open or shorted harness loop in the center restraint circuit
• Damaged connectors under the center seating section

What to do?

Access the center seatbelt reel assembly and test the resistance of the deployment loop. Inspect the wiring paths for pinches or breaks. Replace the load limiter assembly or repair the circuit as necessary.

Symptoms

• Airbag light illuminated on the dashboard
• Side impact deployment capabilities disabled

Common causes

• Defective side-impact impact sensor located inside the left door or B-pillar
• Corroded door-jamb accordion boot wiring harness pins
• Water ingress inside the door shell damaging the sensor

What to do?

Inspect the wiring harness that passes through the door jamb boot for broken wires due to door opening/closing fatigue. Remove the inner door trim panel or B-pillar panel to check the sensor connection for water corrosion. Replace the sensor if water damaged.

Symptoms

• SRS system light stays illuminated
• Frontal crash deployment algorithms compromised

Common causes

• Faulty front crash sensor mounted on the radiator core support frame
• Corroded front sensor plug due to road salt, water, and debris exposure
• Front-end collision damage straining the sensor assembly

What to do?

Locate the front crash sensor behind the front grille or bumper rail. Carefully inspect the yellow plug for moisture or corrosion. Clean the plug contacts thoroughly. If the code persists after contact cleaning, replace the front-impact sensor unit.

Symptoms

• Multiple body electrical failures (power windows, locks, lights)
• SRS or BCM completely unresponsive
• No communication with the body control module

Common causes

• Internal hardware failure inside the Body Control Module (BCM) or SRS module
• Software corruption within the control module
• Voltage spikes or jump-starting errors damaging internal circuits

What to do?

Perform a hard reset by disconnecting the vehicle battery for 30 minutes. Check all power and ground feeds going to the affected module. If power and grounds are good, the module must be reprogrammed or replaced entirely.

Symptoms

• Climate control buttons are completely unresponsive
• AC, heater, or fan speed settings cannot be changed

Common causes

• Faulty HVAC control head or button panel
• Broken or frayed wiring behind the center console
• Loose multi-pin connector on the rear of the climate panel

What to do?

Remove the center dash trim to expose the climate control unit. Verify that the rear connectors are plugged in securely. Use a multi-meter to check for continuity along the button wiring matrix; replace the HVAC control unit if internal circuit board damage is found.

Symptoms

• Slow engine cranking or clicking noises
• Flickering dashboard lights and erratic accessory behavior
• False diagnostic trouble codes appearing in multiple modules

Common causes

• Weak, aged, or failing 12V car battery
• Faulty or undercharging alternator
• Corroded or loose battery terminals and ground cables

What to do?

Test the vehicle battery condition and charge state using a digital battery analyzer. Inspect the battery terminals for corrosion and clean/tighten them. If the battery fails the load test, replace it. Check alternator charging output voltage under load (should be 13.5V to 14.5V).

Symptoms

• Chime does not ring when the key is in the ignition and door is open
• Radio stays on after key removal and door opened
• Power door locks act erratically when key is inserted

Common causes

• Worn out or broken warning switch inside the ignition lock cylinder
• Damaged wiring or pins in the steering column ignition switch connector
• Blown body control module accessory fuse

What to do?

Inspect the ignition lock cylinder switch. Test the key-in-ignition warning switch circuit for continuity when the key is inserted and removed. Replace the mechanical ignition switch or lock cylinder assembly if the contact switch is failed.

Symptoms

• Rear window heater grid fails to clear frost or condensation
• Defogger button indicator light flashes or fails to turn on

Common causes

• Broken heating grid lines on the rear windshield glass
• Faulty rear defogger relay
• Blown defogger fuse
• Corroded or disconnected wiring tab at the edge of the rear glass

What to do?

Check the defogger fuse and swap the relay to test. Inspect the rear window glass for any visible scratches or breaks in the horizontal metallic grid lines. Use a conductive repair kit to patch any grid line breaks, or re-solder the main electrical lead tab if detached.

Symptoms

• Engine cranks but refuses to start
• Anti-theft / security light flashing rapidly on the dashboard

Common causes

• Using an unprogrammed or damaged transponder key
• Defective immobilizer transceiver antenna coil around the ignition barrel
• Wiring defect between the transceiver coil and the instrument cluster/PCM

What to do?

Try starting the vehicle with a known-good spare programmed master key. If the spare works, the original key's transponder chip is defective. If no keys work, test the transceiver ring antenna surrounding the ignition lock cylinder for power and ground, and replace if faulty.

Symptoms

• Engine will not start (immobilizer active)
• Security light flashes a specific code error sequence

Common causes

• Attempting to start the car with an unprogrammed key
• Key transponder code corrupted
• Another RFID chip or key fob on the same keyring interfering with the signal

What to do?

Remove all other RFID cards, building passes, or extra car keys from the keyring and try again. If the issue remains, use an OBD2 tool with key programming capability to re-add/re-program the transponder key to the vehicle's immobilizer module.

Symptoms

• Airbag warning light active on dash
• Passenger airbag status indicator light on the dash panel remains unlit

Common causes

• Blown light bulb or failed LED within the passenger airbag status display panel
• Damaged wiring harness leading to the center dash display panel
• Faulty Body Control Module (BCM) or SRS module logic

What to do?

Remove the center dash trim panel housing the passenger airbag status light indicator. Test for voltage arriving at the bulb/LED harness when the ignition is switched on. If voltage is present but the LED fails to light up, replace the light/switch assembly.

Symptoms

• SRS light permanently illuminated on the dashboard
• Driver frontal airbag completely disabled

Common causes

• Open circuit due to broken internal ribbon cable in the clock spring
• Unplugged or loose connector at the back of the driver's steering wheel airbag
• Corrosion or high resistance in the steering wheel wiring harness

What to do?

Ensure battery is completely disconnected. Check the connections behind the driver's airbag module. Use a specialized SRS simulator resistor tool to test the circuit loop; if the fault shifts to stored after adding the resistor, replace the defective clock spring.

Symptoms

• Airbag warning lamp illuminated
• Passenger side deployment logic default disabled

Common causes

• Faulty front passenger seat pressure sensor or module
• Wiring mismatch or poor ground connection underneath the passenger seat
• Recent deep interior cleaning or heavy weight causing sensor deformation

What to do?

Check under-seat wiring for loose connections. Use a scan tool to view real-time live data from the Occupant Classification System module to see if weight registers. Perform a zero-point recalibration procedure. If the weight remains static or errant, replace the OCS sensor pad.

Symptoms

• SRS system light stays lit
• Pretensioners fail self-test sequence upon startup

Common causes

• High resistance in the seatbelt pretensioner circuit
• Corroded wiring plug connections underneath the front seats
• Damaged seatbelt retractor assembly containing the explosive squib

What to do?

Examine the yellow wiring connections underneath the affected seat. Disconnect, clean the metal contact pins with specialized contact cleaner, re-seat securely, and clear the fault codes. If the code returns, measure squib resistance (must match factory specifications, typically 2-3 ohms).

Symptoms

• Airbag light flashing or staying solid on the instrument cluster
• Entire SRS safety framework in safety/shutdown fallback mode

Common causes

• Short to ground or voltage in one of the airbag deployment loops
• Faulty SRS control module
• Corroded multi-pin central restraint module plug

What to do?

Connect an advanced diagnostic scanner to pinpoint which sub-loop (driver, passenger, side, curtain) is returning the status error. Inspect the wiring pins of that specific sub-loop for physical short circuits or harness chafing against the vehicle frame.

Symptoms

• Driver's heated seat fails to warm up
• Heated seat switch button indicator lights up then turns off immediately

Common causes

• Broken heating grid wire element inside the seat cushion foam
• Defective heated seat control module
• Damaged or pinched wire under the driver seat frame

What to do?

Locate the seat heating element power plug under the driver's seat. Use a digital multi-meter to check for continuity/ohms across the element leads. If the meter displays an open circuit (OL), the heating element embedded inside the seat fabric/leather must be replaced.

Symptoms

• A newly installed module (BCM, SRS, or Cluster) fails to operate
• Erratic vehicle network behaviors and mismatched options features

Common causes

• Installing a replacement module without programming it to the car
• Mismatched VIN or configuration string inside the vehicle network
• Incorrect variant configuration selected during setup

What to do?

Connect a manufacturer-specific diagnostic computer (e.g., Ford IDS, GM Tech2/GDS2). Execute a module configuration setup, parameter reset, or programmable module installation (PMI) procedure to download the correct As-Built configuration data into the unit.

Symptoms

• No air blowing out of any climate control vents
• Blower motor runs only on high speed or erratically cuts off

Common causes

• Burnt out cabin fan blower motor
• Failed blower motor resistor pack or control module
• Blown high-amperage HVAC blower fuse

What to do?

Check the primary blower motor fuse. If intact, locate the blower motor under the passenger footwell and check for 12V power at its harness while turning the fan speed up. If power is present but the fan does not spin, tap it gently; if it stays dead, replace the blower motor. If it only works on maximum speed, replace the resistor.

Symptoms

• Vehicle security warning active
• The engine will crank but cannot achieve combustion

Common causes

• Faulty immobilizer module or smart key module
• Open or short circuit in the communication wire between the anti-theft module and PCM
• Corrupted rolling key code sync

What to do?

Perform an anti-theft system parameter reset using a compatible diagnostic scanner. Check wiring schematics to verify communication link integrity between the security transponder ring, body module, and engine computer. Repair any open communication lines.

Symptoms

• Steering wheel remains locked when pressing the start button
• The car fails to turn on ignition power (No accessory/Run mode)
• "Steering Lock Malfunction" warning on the multi-information display

Common causes

• Failed Electronic Steering Column Lock (ESCL) actuator motor
• Internal circuit board failure within the steering lock module
• Blown fuse for the steering column lock circuit

What to do?

Gently wiggle the steering wheel back and forth while pressing the engine start button to relieve pressure on the locking pin mechanism. If it stays jammed, check the ESCL fuse. If power is reaching the actuator unit but it refuses to release, the electronic steering column lock module requires physical replacement and programming.

Symptoms

• Immobilizer system active; security light on solid
• Certain modules (like radio or cluster) display "LOCKED"

Common causes

• Installing a used, un-cleared salvage module from a different car
• Incorrect VIN manual entry during a module programming event

What to do?

The module's stored VIN must match the vehicle's true VIN across the CAN bus network. Connect a proper diagnostic pass-thru tool and re-flash the module with the correct vehicle identification number using the manufacturer's subscription programming software.

Symptoms

• Engine cranks but cuts out after 2 seconds or fails to crank entirely
• Security indicator light blinking quickly

Common causes

• Short circuit to ground in the anti-theft sensor line
• Faulty pass-key key cylinder or transponder ring
• Corroded connectors on the security harness module feed

What to do?

Trace the security data line from the ignition cylinder back to the body module. Check for short circuits to ground using a multi-meter. Ensure the harness is not rubbing against sharp metal structural brackets behind the steering wheel.

Symptoms

• Rough or unstable idle
• Reduced engine power
• Poor fuel economy
• Occasional hard starts

Common causes

• Faulty VVT (variable valve timing) solenoid
• Low or dirty engine oil restricting solenoid flow
• Stretched timing chain
• Wiring or connector issue at the solenoid
• Worn camshaft phaser

What to do?

Start with an oil and filter change using the manufacturer's specified viscosity - sludge and wrong-weight oil cause many P0014 cases. If the code persists, test the VVT solenoid and inspect for chain stretch. Do not ignore this code; severe over-advance can damage valves.

Symptoms

• Rough or unstable idle
• Hard starting or extended cranking
• Engine knock or rattle on startup
• Reduced power

Common causes

• Stretched timing chain
• Worn camshaft phaser (VVT) on the exhaust cam
• Low oil pressure starving the VVT system
• Faulty camshaft or crankshaft position sensor
• Skipped timing chain or guide failure

What to do?

Check oil level and condition immediately - this code often points to oil starvation in the VVT system. View live data for crank vs cam position; a consistent offset confirms a timing issue. This is a serious code: continued driving can lead to valve-to-piston contact.

Symptoms

• Poor acceleration or hesitation
• Rough idle and stalling
• Reduced fuel economy
• Black smoke from the exhaust in some cases

Common causes

• Dirty MAF sensor element
• Vacuum or intake leak after the MAF
• Clogged or aftermarket air filter shedding fibers
• Faulty MAF sensor
• Damaged intake boot

What to do?

Replace the air filter and clean the MAF sensor with dedicated MAF cleaner (never carb or brake cleaner). Inspect the intake boot between the MAF and throttle body for tears. If the code returns with clean intake plumbing, replace the MAF.

Symptoms

• Check engine light
• Increased fuel consumption, especially on cold starts
• Slight rough running until the engine warms up
• Slow to enter closed-loop operation

Common causes

• Failed heater element inside the upstream O2 sensor
• Blown O2 heater fuse
• Damaged wiring or melted connector
• Open circuit in the heater control line

What to do?

Check the heater fuse and the connector at the sensor first. Measure the heater resistance with a multimeter (compare to spec - usually a few ohms). If wiring and fuse are good but resistance is out of range, replace the upstream O2 sensor on bank 1.

Symptoms

• Check engine light
• Slightly reduced fuel economy
• Slow to reach closed-loop operation on cold starts
• No major driveability issues

Common causes

• Failed heater element inside the downstream O2 sensor
• Blown O2 heater fuse
• Damaged wiring or connector to the sensor
• PCM driver issue (rare)

What to do?

Check the O2 sensor heater fuse first - a simple fuse replacement is sometimes all that is needed. Inspect the connector for corrosion or melted pins, common on sensors near hot exhaust. If wiring is good, replace the downstream O2 sensor.

Symptoms

• Rough idle and stalling
• Hesitation under acceleration
• Lack of power
• Possible misfires at idle

Common causes

• Vacuum leak in intake hose or gasket
• Dirty or failing MAF sensor
• Weak fuel pump or clogged fuel filter
• Leaking or restricted fuel injector
• Bad oxygen sensor reporting wrong values

What to do?

Inspect the intake plumbing for cracked hoses and a torn intake boot - vacuum leaks are the most common cause. Clean the MAF sensor with proper MAF cleaner, then verify fuel pressure under load. Live data showing both short and long-term fuel trim above +10% confirms the lean condition.

Symptoms

• Poor fuel economy
• Black smoke from the exhaust
• Strong fuel smell
• Rough idle and fouled spark plugs

Common causes

• Leaking fuel injector dripping into a cylinder
• Faulty or contaminated MAF sensor
• Excessive fuel pressure from a stuck regulator
• Clogged air filter restricting airflow
• Failing upstream oxygen sensor

What to do?

Check fuel trims on a scan tool - long-term trim well below zero confirms a rich condition. Inspect the air filter and MAF sensor, then test fuel pressure. If injectors are suspect, a balance test or current ramp can identify a stuck-open injector.

Symptoms

• Significant loss of power, especially on acceleration
• Limp mode kicking in
• Whistling or hissing from the engine bay
• Black smoke under load

Common causes

• Boost or intercooler hose leak
• Faulty wastegate or actuator
• Failing turbocharger
• Clogged intercooler or intake
• Bad boost pressure sensor

What to do?

Inspect every boost pipe and intercooler hose for cracks, splits, and loose clamps - this is the most common cause. Check the wastegate actuator for free movement and proper rod travel. Use a scan tool to compare requested vs actual boost pressure to confirm the underboost.

Symptoms

• Rough idle and shaking at stops
• Hesitation or stumbling on acceleration
• Noticeable loss of power
• Check engine light flashing under load

Common causes

• Worn or fouled spark plugs
• Failing ignition coil packs
• Vacuum or intake manifold leak
• Clogged or leaking fuel injector
• Low fuel pressure or weak fuel pump

What to do?

Avoid hard driving while a misfire is active to protect the catalytic converter. Start with the basics: inspect spark plugs and coils, then scan for cylinder-specific misfire codes (P0301-P0308) to narrow the source. If no single cylinder is flagged, check for vacuum leaks and fuel pressure before replacing parts.

Symptoms

• Rough idle that smooths out at higher RPM
• Hesitation when accelerating
• Flashing check engine light under load
• Sulfur or raw fuel smell

Common causes

• Worn or fouled spark plug on cylinder 2
• Failing ignition coil on that cylinder
• Faulty or clogged fuel injector
• Low compression from valve or piston ring wear

What to do?

Swap the coil and spark plug from cylinder 2 with a neighbouring cylinder, clear the code, and drive. If the misfire follows the parts, you have your culprit. If it stays on cylinder 2, the injector or a compression issue is likely - run a compression or leakdown test.

Symptoms

• Hard starting or no-start condition
• Intermittent stalling while driving
• Sudden loss of power
• Tachometer drops to zero while running

Common causes

• Failed crankshaft position sensor
• Damaged sensor wiring or corroded connector
• Metal debris stuck to the sensor tip
• Damaged reluctor wheel on the crankshaft
• PCM issue (rare)

What to do?

Inspect the connector for damage and check the sensor for metal fuzz on the tip (often picked up from clutch dust on manuals or transmission debris). Test the sensor signal with a scope or scan tool during cranking. Replacement is usually straightforward once confirmed.

Symptoms

• Pinging or knocking under load
• Rough idle or stalling
• Failed emissions test
• Slight loss of power

Common causes

• Carbon-clogged EGR valve or passages
• Stuck EGR valve
• Faulty DPFE or EGR position sensor
• Failed EGR vacuum solenoid
• Blocked EGR tube

What to do?

Remove and inspect the EGR valve - carbon buildup is the most frequent cause and often cleanable. Check the EGR passages in the intake manifold and clean them out as well. Test the DPFE or position sensor against spec before replacing the valve itself.

Symptoms

• Check engine light
• Slight loss of power
• Rotten egg or sulfur smell from exhaust
• Reduced fuel economy

Common causes

• Failing catalytic converter on bank 2
• Faulty downstream (rear) oxygen sensor
• Exhaust leak before or between sensors
• Engine running rich or lean over time damaging the cat
• Internal engine problems causing oil/coolant burn

What to do?

Do not jump straight to replacing the catalytic converter. First, fix any other active codes (especially fuel trim or misfire codes), then check the rear O2 sensor signal - it should show much less activity than the front sensor. Inspect for exhaust leaks before condemning the cat.

Symptoms

• Check engine light
• Faint fuel smell, especially after refueling
• No impact on driving

Common causes

• Loose, damaged, or wrong-type fuel cap
• Cracked or disconnected EVAP hose
• Faulty purge or vent valve
• Cracked charcoal canister
• Leaking O-ring at fuel filler neck

What to do?

Start by tightening or replacing the fuel cap and clearing the code - this resolves a large share of P0440 cases. If the code returns, have the EVAP system smoke tested, since most leaks are too small to find by sight or sound.

Symptoms

• Check engine light
• Slight rough running at idle in some cases
• Usually no impact on driving

Common causes

• Stuck-open or stuck-closed purge valve
• Blocked or kinked EVAP hose
• Faulty canister vent valve
• Failing fuel tank pressure sensor

What to do?

Test the purge valve by applying vacuum - it should hold when closed and release when commanded open. Inspect the hose from the purge valve to the intake for kinks or blockage. If valves test fine, check the EVAP system for leaks with a smoke test.

Symptoms

• Check engine light
• Occasional faint fuel odor
• No impact on driving

Common causes

• Loose or worn fuel cap
• Small crack in an EVAP hose
• Faulty purge valve or vent solenoid
• Damaged O-ring on the fuel filler neck

What to do?

Try tightening or replacing the fuel cap first - this clears the code on a surprising number of vehicles. If it returns within a few drive cycles, have a shop smoke-test the EVAP system to pinpoint the leak.

Symptoms

• Check engine light
• Hissing sound from fuel tank area after fill-up
• Possible difficulty filling the tank
• Faint fuel odor

Common causes

• Failed canister vent valve solenoid
• Corroded or damaged wiring/connector at the vent valve
• Open or short in the control circuit
• PCM control issue (rare)

What to do?

The vent valve usually sits near the charcoal canister, often under the vehicle and exposed to weather. Inspect its connector for corrosion - this is a very common cause. Test the solenoid for resistance and command it on/off with a scan tool. Replace if it fails to actuate.

Symptoms

• Check engine light
• Faint fuel smell near the rear of the vehicle
• Usually no driveability issues

Common causes

• Loose, damaged, or missing fuel cap
• Cracked or disconnected EVAP hose
• Failed canister purge or vent valve
• Cracked charcoal canister

What to do?

Start with the cheapest fix: remove and reseat the fuel cap, or replace it if the seal is worn. If the code returns, a smoke test of the EVAP system will quickly locate the leak. The system is sealed at very low pressure, so visual inspection alone often misses cracks.