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.

Emissions System 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 25–48 of 515

Most searched first

P041EEGR Temperature Sensor B Circuit Intermittent/ErraticCheck soonEmissions System30–120 minutes for initial diagnosisP041E relates to egr temperature sensor b circuit intermittent/erratic. Check the fault conditions and vehicle-specific procedure before replacing parts.P0422Main Catalyst Efficiency Below Threshold (Bank 1)Low priorityEmissions System30–90 minutes for initial diagnosisP0422 indicates the catalyst monitor reports that main-catalyst efficiency on Bank 1 is below the calibrated threshold. Learn what to inspect before replacing parts.P0423Heated Catalyst Efficiency Below Threshold (Bank 1)Low priorityEmissions System30–90 minutes for initial diagnosisP0423 indicates the heated-catalyst monitor reports efficiency below the calibrated threshold on Bank 1. Learn what to inspect before replacing parts.P0424Heated Catalyst Temperature Below Threshold (Bank 1)Check soonEmissions System30–90 minutes for initial diagnosisP0424 indicates the monitored heated-catalyst temperature on Bank 1 is below the expected threshold. Learn what to inspect before replacing parts.P0425Catalyst Temperature Sensor Circuit (Bank 1, Sensor 1)Check soonEmissions System30–90 minutes for initial diagnosisP0425 indicates the control module detected a fault in the Bank 1 Sensor 1 catalyst-temperature-sensor circuit. Learn what to inspect before replacing parts.P0426Catalyst Temperature Sensor Circuit Range/Performance (Bank 1, Sensor 1)Check soonEmissions System30–90 minutes for initial diagnosisP0426 indicates the Bank 1 Sensor 1 catalyst-temperature signal is outside its expected range or does not respond plausibly. Learn what to inspect before replacing parts.P0427Catalyst Temperature Sensor Circuit Low (Bank 1, Sensor 1)Check soonEmissions System30–90 minutes for initial diagnosisP0427 indicates the Bank 1 Sensor 1 catalyst-temperature sensor circuit signal is below the expected electrical range. Learn what to inspect before replacing parts.P0428Catalyst Temperature Sensor Circuit High (Bank 1, Sensor 1)Check soonEmissions System30–90 minutes for initial diagnosisP0428 indicates the Bank 1 Sensor 1 catalyst-temperature sensor circuit signal is above the expected electrical range. Learn what to inspect before replacing parts.P0429Catalyst Heater Control Circuit (Bank 1)Check soonEmissions System30–90 minutes for initial diagnosisP0429 indicates the control module detected a fault in the Bank 1 catalyst-heater control circuit. Learn what to inspect before replacing parts.P042ACatalyst Temperature Sensor Circuit Bank 1 Sensor 2Check soonEmissions System30–120 minutes for initial diagnosisP042A relates to catalyst temperature sensor circuit bank 1 sensor 2. Check the fault conditions and vehicle-specific procedure before replacing parts.P042BCatalyst Temperature Sensor Circuit Range/Performance Bank 1 Sensor 2Check soonEmissions System30–120 minutes for initial diagnosisP042B relates to catalyst temperature sensor circuit range/performance bank 1 sensor 2. Check the fault conditions and vehicle-specific procedure before replacing parts.P042CCatalyst Temperature Sensor Circuit Low Bank 1 Sensor 2Check soonEmissions System30–120 minutes for initial diagnosisP042C relates to catalyst temperature sensor circuit low bank 1 sensor 2. Check the fault conditions and vehicle-specific procedure before replacing parts.P042DCatalyst Temperature Sensor Circuit High Bank 1 Sensor 2Check soonEmissions System30–120 minutes for initial diagnosisP042D relates to catalyst temperature sensor circuit high bank 1 sensor 2. Check the fault conditions and vehicle-specific procedure before replacing parts.P042EEGR A Control Stuck OpenCheck soonEmissions System30–120 minutes for initial diagnosisP042E relates to egr a control stuck open. Check the fault conditions and vehicle-specific procedure before replacing parts.P042FEGR A Control Stuck ClosedCheck soonEmissions System30–120 minutes for initial diagnosisP042F relates to egr a control stuck closed. Check the fault conditions and vehicle-specific procedure before replacing parts.P0430Catalyst System Efficiency Below Threshold Bank 2Emissions SystemP0430 catalytic converter code for Bank 2. Same as P0420 but for the other side. Learn diagnosis and repair options.P0431Warm Up Catalyst Efficiency Below Threshold Bank 2Low priorityEmissions System30–120 minutes for initial diagnosisP0431 indicates a fault related to warm up catalyst efficiency below threshold bank 2. Learn the likely causes and a practical diagnostic order before replacing parts.P0432Main Catalyst Efficiency Below Threshold (Bank 2)Low priorityEmissions System30–90 minutes for initial diagnosisP0432 indicates the catalyst monitor reports that main-catalyst efficiency on Bank 2 is below the calibrated threshold. Learn what to inspect before replacing parts.P0433Heated Catalyst Efficiency Below Threshold (Bank 2)Low priorityEmissions System30–90 minutes for initial diagnosisP0433 indicates the heated-catalyst monitor reports efficiency below the calibrated threshold on Bank 2. Learn what to inspect before replacing parts.P0434Heated Catalyst Temperature Below Threshold Bank 2Check soonEmissions System30–120 minutes for initial diagnosisP0434 indicates a fault related to heated catalyst temperature below threshold bank 2. Learn the likely causes and a practical diagnostic order before replacing parts.P0435Catalyst Temperature Sensor Circuit Bank 2 Sensor 1Check soonEmissions System30–120 minutes for initial diagnosisP0435 relates to catalyst temperature sensor circuit bank 2 sensor 1. Check the fault conditions and vehicle-specific procedure before replacing parts.P0436Catalyst Temperature Sensor Circuit Range/Performance Bank 2 Sensor 1Check soonEmissions System30–120 minutes for initial diagnosisP0436 relates to catalyst temperature sensor circuit range/performance bank 2 sensor 1. Check the fault conditions and vehicle-specific procedure before replacing parts.P0437Catalyst Temperature Sensor Circuit Low Bank 2 Sensor 1Check soonEmissions System30–120 minutes for initial diagnosisP0437 relates to catalyst temperature sensor circuit low bank 2 sensor 1. Check the fault conditions and vehicle-specific procedure before replacing parts.P0438Catalyst Temperature Sensor Circuit High Bank 2 Sensor 1Check soonEmissions System30–120 minutes for initial diagnosisP0438 relates to catalyst temperature sensor circuit high bank 2 sensor 1. Check the fault conditions and vehicle-specific procedure before replacing parts.