OBD Exhaust Heat Exchanger Exhaust Bypass Valve B Control Circuit High
What it means
P23A4 stands for Exhaust Heat Exchanger Exhaust Bypass Valve B Control Circuit High. P23A4 is a P code, so the fault sits in the engine, transmission and emissions systems. For P23A4, the second digit places it in ignition and misfire. For P23A4, work through the cause list below, cheapest checks first.
Where it lives
For P23A4, start at the valve the description names.
What to check first
For P23A4, read the stored codes from every module, not just the engine, because related codes often name the same fault more precisely.
Check these first
- P23A4: Failing ignition coil, spark plug, or spark plug wire
- P23A4: Faulty crankshaft or camshaft position sensor
- P23A4: Wiring or connector damage in the ignition circuit
- P23A4: Low compression or engine mechanical wear
- P23A4: Incorrect ignition timing or a stretched timing chain
What to do next
P23A4 reports from the ignition and misfire system. These steps cover P23A4 in general, and the exact cause on your vehicle can differ from the cause named above.
- P23A4: Read misfire counts and freeze frame data with an OBD-II scanner
- P23A4: Test spark output and inspect spark plugs and coils
- P23A4: Check crankshaft and camshaft position sensor signals while cranking
- P23A4: Swap suspect ignition parts between cylinders to see if the fault moves
- P23A4: Compression test if the issue persists on the same cylinder
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Updated
Generic SAE J2012 definition. Last updated 2026-08-30.