Diagnostic library

Find an OBD2 code

Search the code from your scanner, then narrow the library by system, severity, or code family.

9,253 diagnostic guides

Sort

Find codes by symptomChoose what you notice to search matching code guides.

Rough idle or shakingVibration while stopped Hard to startLong cranking or no-start Engine stallsCuts out at idle or on the road Hesitates or loses powerSlow response when accelerating Battery light is onCharging system warning Harsh gear changesDelayed or rough shifting

A symptom can have several causes. Treat matching codes as clues and follow the diagnostic checks in each guide.

P · Powertrain Clear all

Quick browse

Choose a vehicle system

Engine1049 Emissions515 Fuel1016 Sensors & Electronics2110 Transmission866 Electrical & Charging1797 Body & Restraints193 Chassis & Brakes479 Network & Communication1228

FiltersSeverity · family

Severity

All severities9253 Low priority305 Check soon8256 Urgent621

Code family

All families9253 P · Powertrain7353 B · Body193 C · Chassis479 U · Network1228

Vehicle coverage

These are generic OBD2 definitions. Exact make, model, engine, and year compatibility will appear after vehicle-fitment data is added.

Diagnostic codes

Showing 3961–3984 of 7353

Most searched first

P21B4NOx Adsorber - Over Temperature Bank 1UrgentSensors & Electronics30–120 minutes for initial diagnosisP21B4 relates to nox adsorber - over temperature bank 1. Check the fault conditions and vehicle-specific procedure before replacing parts.P21B5NOx Adsorber - Over Temperature Bank 2UrgentSensors & Electronics30–120 minutes for initial diagnosisP21B5 relates to nox adsorber - over temperature bank 2. Check the fault conditions and vehicle-specific procedure before replacing parts.P21B6Cold Start Cylinder 1 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21B6 relates to cold start cylinder 1 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21B7Cold Start Cylinder 2 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21B7 relates to cold start cylinder 2 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21B8Cold Start Cylinder 3 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21B8 relates to cold start cylinder 3 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21B9Cold Start Cylinder 4 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21B9 relates to cold start cylinder 4 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21BACold Start Cylinder 5 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21BA relates to cold start cylinder 5 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21BBCold Start Cylinder 6 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21BB relates to cold start cylinder 6 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21BCCold Start Cylinder 7 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21BC relates to cold start cylinder 7 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21BDCold Start Cylinder 8 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21BD relates to cold start cylinder 8 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21BECold Start Cylinder 9 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21BE relates to cold start cylinder 9 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21BFCold Start Cylinder 10 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21BF relates to cold start cylinder 10 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C0Cold Start Cylinder 11 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21C0 relates to cold start cylinder 11 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C1Cold Start Cylinder 12 Injection TimingCheck soonFuel System30–120 minutes for initial diagnosisP21C1 relates to cold start cylinder 12 injection timing. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C2Reductant Heater Relay Control Circuit/OpenCheck soonElectrical & Charging System30–120 minutes for initial diagnosisP21C2 relates to reductant heater relay control circuit/open. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C3Reductant Heater Relay Control Circuit LowCheck soonElectrical & Charging System30–120 minutes for initial diagnosisP21C3 relates to reductant heater relay control circuit low. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C4Reductant Heater Relay Control Circuit HighCheck soonElectrical & Charging System30–120 minutes for initial diagnosisP21C4 relates to reductant heater relay control circuit high. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C5Reductant Level Sensor A StuckCheck soonSensors & Electronics30–120 minutes for initial diagnosisP21C5 relates to reductant level sensor a stuck. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C6Reductant Level Sensor B StuckCheck soonSensors & Electronics30–120 minutes for initial diagnosisP21C6 relates to reductant level sensor b stuck. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C7Reductant Control Module Power Relay/Relays Control Circuit/OpenCheck soonElectrical & Charging System30–120 minutes for initial diagnosisP21C7 relates to reductant control module power relay/relays control circuit/open. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C8Reductant Control Module Power Relay/Relays Control Circuit LowCheck soonElectrical & Charging System30–120 minutes for initial diagnosisP21C8 relates to reductant control module power relay/relays control circuit low. Check the fault conditions and vehicle-specific procedure before replacing parts.P21C9Reductant Control Module Power Relay/Relays Control Circuit HighCheck soonElectrical & Charging System30–120 minutes for initial diagnosisP21C9 relates to reductant control module power relay/relays control circuit high. Check the fault conditions and vehicle-specific procedure before replacing parts.P21CAReductant Control Module Supply Voltage CircuitCheck soonElectrical & Charging System30–120 minutes for initial diagnosisP21CA relates to reductant control module supply voltage circuit. Check the fault conditions and vehicle-specific procedure before replacing parts.P21CBReductant Control Module Supply Voltage LowCheck soonElectrical & Charging System30–120 minutes for initial diagnosisP21CB relates to reductant control module supply voltage low. Check the fault conditions and vehicle-specific procedure before replacing parts.