P1375 KOER Spark Test RPM Low
The P1375 code is set during the Key On Engine Running (KOER) self-test when the PCM commands a momentary spark retard to verify idle control authority and engine mechanical response. If the RPM increase during this spark advance test does not meet the expected threshold, it indicates a lack of response from the ignition system, air/fuel mixture, or basic engine mechanicals.
01. Most Common Causes
- Worn, fouled, or incorrectly gapped spark plugs
- Faulty ignition coils or damaged spark plug wires
- Unmetered vacuum leaks (intake manifold, hoses, throttle body gasket)
- Clogged or leaking fuel injectors
- Low fuel pressure (failing pump, clogged filter, bad regulator)
- Erratic crankshaft position (CKP) or camshaft position (CMP) sensor signal
- Internal mechanical issues: low compression, incorrect valve timing
- Dirty throttle body or stuck idle air control (IAC) / electronic throttle control (ETC)
- Faulty PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or stalling during KOER test
- Poor acceleration or hesitation
- Possible hard starting
03. Step-by-Step Diagnosis
Scan for codes and freeze frame data; note if other codes are present.
Perform KOER test and monitor RPM response; compare to specifications.
Inspect spark plugs for wear, fouling, or incorrect gap; replace if needed.
Check ignition coils and wires for damage or misfire; test with spark tester.
Test fuel pressure and volume; inspect for vacuum leaks using smoke machine.
Verify CKP and CMP sensor signals with oscilloscope; check for mechanical issues (compression test, timing check).
Clean throttle body and IAC/ETC; perform idle relearn if necessary.
1. Frequently Asked Questions
Is it safe to drive?▼
The vehicle may be drivable but with reduced performance and potential for stalling. It is recommended to diagnose and repair promptly to avoid further damage.
How much does it cost to fix?▼
Repair costs vary widely depending on the cause, typically ranging from $100 for a simple spark plug replacement to $800+ for ignition coils or fuel system repairs.