Not saying this is valid, but I did it for my own curiosity. AI reply below.
Likely cause — electrical fault in the turbo/intercooler electric coolant pump circuit (wiring/connector or pump) and possibly a related ECU/BSI input fault.
What the codes mean (concise)
- P023B / P023C — Charge-air (turbo/intercooler) coolant pump control circuit: low (short to earth) and high (short to positive). These indicate the ECU is seeing both over-voltage and under-voltage / short conditions on the pump circuit or its sensor feedback.
- P1655 / P1656 — Engine running system info / starter-disable type faults showing both short-to-positive and short-to-earth on the related control/communication line — suggests the same wiring loom/connector or a module input is unstable.
Most probable faults (ranked)
- Damaged wiring or chafed insulation around the intercooler/coolant-pump harness (especially where it routes near the cam cover if that was recently worked on).
- Poor connector contact or contaminated/bent pins at the coolant-pump plug or at the engine ECU/BSI connector.
- Failed electric coolant pump (internal shorting) or its internal control electronics.
- Faulty ECU/BSI (less likely) or temporary re-learn/communication error after work.
Recommended checks (step-by-step)
- With battery disconnected, visually inspect the coolant pump connector and wiring from pump to ECU for pin damage, corrosion, melted insulation, or recent disturbed clips.
- Wiggle-test wiring and connectors while scanning live data (or have garage do this) to reproduce voltage errors.
- Measure with a multimeter: check for short to earth and short to +12V at the pump connector pins (engine off). Compare to expected: one pin should have switched supply when commanded, the other ground/return or signal.
- If wiring/connector are good, bench-test or swap in a known-good pump (or temporarily supply correct voltage to pump) to confirm pump operation.
- If pump and wiring test OK, have ECU/BSI inputs tested (dealer-level diagnostic), clear codes and re-run while monitoring.
Immediate precautions
- Don’t ignore: if the pump is not running or circuit is unstable you can get overheating / turbo charge-air cooling loss and limp mode.
- Avoid repeated cranking if electrical shorts are suspected.
What to tell the garage
- Ask them to focus on the intercooler/turbo electric coolant pump circuit: inspect wiring and connectors near the cam cover/engine loom, measure for shorts to + and earth at the pump connector, and confirm pump draws correct current. If wiring/connector OK, replace the pump; if still present, request ECU/BSI module diagnostic.
If you want, I can give a short pinout checklist for the RCZ pump connector and expected voltages (assume engine off/on) — tell me your engine code/year and I’ll provide it.
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