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9,253 diagnostic guides

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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.

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

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Severity

All severities9253 Low priority305 Check soon8256 Urgent621

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

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Diagnostic codes

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P0420Catalyst System Efficiency Below ThresholdLow priorityEmissions System60–150 minutesDiagnose P0420 catalyst efficiency below threshold on Bank 1. Learn what O2 sensor data can show and what to check before replacing the catalytic converter.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.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.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.P0421Warm Up Catalyst Efficiency Below Threshold Bank 1Emissions SystemUnderstand P0421 catalyst code. Learn about warm-up catalyst monitoring and efficiency testing.