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DTC codes / Mazda codes / P1358

P1358 · MazdaIgnition Diagnostic Monitor Signal Out Of Self Test Range

P1358 on Mazda vehicles means the powertrain control module (PCM) has detected that the ignition diagnostic monitor (IDM) signal is outside its expected self-test range during the key-on engine-off self-check. The IDM circuit is how the PCM verifies that the ignition coil primary circuit is switching correctly, so this code points to a fault in that feedback path rather than a misfire or a dead coil.

SystemPowertrain
Code typeMazda specific
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • Occasional rough idle or slight hesitation if the IDM fault is intermittent.
  • Hard starting or a no-start condition in severe cases where the ignition feedback is lost completely.
  • A stumble or momentary loss of power under acceleration if the PCM cannot confirm coil firing.
  • No drivability complaints at all in many cases, because the IDM signal is a diagnostic monitor and not the primary trigger for the coils.

Common causes, most likely first

  1. Faulty ignition coil with an internal open or short in the primary winding or the IDM feedback circuit.
  2. Damaged or corroded wiring between the ignition coil IDM terminal and the PCM connector.
  3. Poor ground connection at the ignition coil mounting or engine block ground strap.
  4. Failed ignition condenser (capacitor) on the coil circuit causing signal noise.
  5. PCM internal fault in the IDM monitoring circuit, which is rare but possible.
  6. Aftermarket ignition components or a poor previous repair that altered the IDM signal characteristics.
  7. Moisture intrusion into the coil connector or PCM connector causing intermittent signal loss.

How to diagnose and fix it

  1. Clear the code and perform a key-on engine-off self-test to see if P1358 returns immediately, which confirms a hard fault in the IDM circuit.
  2. Inspect the ignition coil connector and the PCM connector for corrosion, pushed pins, or loose terminals, and repair any damaged wiring.
  3. Measure resistance of the ignition coil primary and secondary windings against the Mazda service specification for your engine, and replace the coil if out of range.
  4. Check the ignition coil ground circuit for excessive voltage drop while cranking, and clean or repair the ground point if resistance is high.
  5. Test the IDM signal wire from the coil to the PCM for continuity and short-to-ground or short-to-power, repairing the harness as needed.
  6. Substitute a known-good ignition coil and re-run the self-test to see if P1358 clears, which isolates the fault to the coil.
  7. If all external circuits and components test good, follow Mazda diagnostic flow for PCM internal IDM circuit testing before condemning the PCM.

What the IDM self-test really checks

  • P1358 is set during the key-on engine-off self-test, so a coil that works perfectly while running can still trigger this code if its IDM feedback is out of range at rest.
  • Many technicians replace the ignition coil only to find the code returns because the real problem is a corroded ground strap on the engine block that shifts the IDM voltage reference.
  • A weak or failing ignition condenser on the coil circuit can distort the IDM signal enough to set P1358 without any misfire or driveability symptom.
  • Aftermarket coils with different internal suppression can produce an IDM signal that the Mazda PCM rejects, so sticking with the original-equipment coil design avoids repeat codes.
  • This code does not mean the coil is not firing; it means the PCM cannot verify the firing event through the diagnostic monitor, so chasing a misfire is the wrong path.

Can I keep driving with P1358?

You can usually continue driving if the only symptom is the check engine light, but avoid hard acceleration and long trips until the fault is diagnosed. If the engine starts hard, misfires, or stalls, stop driving and have the ignition system inspected promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Mazda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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