Code
P1356
LINCOLN
P — Powertrain
Loss of Ignition Diagnostic Module Input to PCM
Views:
UK: 25
EN: 35
RU: 28
AI status
Completed
Completed
100%
Causes
- Open or short in IDM-to-PCM wiring/harness
- Poor or corroded connector/terminal at IDM or PCM
- Faulty Ignition Diagnostic Module (IDM) or ignition coil assembly with integrated IDM
- Blown fuse or lost power/ground to IDM or PCM
- Intermittent connection (wire chafe, bent pins, water intrusion)
- PCM hardware or internal software fault
Symptoms
- Malfunction Indicator Lamp (MIL) on
- Engine misfire or rough idle
- Hard start or no-start condition
- Reduced engine power, hesitation or stumbling
- Intermittent stalls or poor drivability
- Possible multiple ignition/coil-related codes present
What to check
- Read stored and pending codes and freeze-frame with a scan tool
- Verify battery voltage (stable ~12.6 V at rest) and charging system voltage while cranking/running
- Visually inspect IDM, coil pack and PCM connectors for corrosion, bent pins, water, or damage
- Check fuses related to IGN/ECM/coil power
- Scan for related ignition and cam/crank sensor codes (may indicate upstream timing/sensor faults)
- Monitor live data for IDM/ignition related PID values while cranking/running
Signal parameters
- Signal type: digital pulse (IDM confirmation of coil firing); pulse present during cranking and engine run
- Voltage levels: typically a pulsed 0 V to supply reference level (0–5 V or up to vehicle supply depending on system) — check service data for exact values
- Pulse rate: proportional to engine speed (one pulse per ignition event per monitored coil)
- Expected behavior: clean repetitive pulses that correspond to cylinder firings during crank/run; no pulse = fault
Diagnostic algorithm
- Record freeze-frame data and all stored codes; note conditions when DTC set (crank, run, temp).
- Verify battery and charging voltages; weak battery can cause erroneous signals. Replace or charge as needed.
- Inspect IDM/coil pack and PCM connectors; repair corrosion, damaged seals, or bent pins. Ensure secure mating.
- Check related fuses and power/ground circuits for continuity and correct voltage at the IDM connector (with key ON/engine cranking).
- Back-probe the IDM signal circuit at the coil/module while cranking; look for pulsed signal with a scope or a digital multimeter (frequency/pulse presence).
- If no pulse at IDM, trace continuity from IDM connector to PCM connector; check for short to battery or ground. Repair wiring faults.
- If wiring and connectors are good but no IDM pulse, swap or replace the ignition module/coil pack (IDM) if a known-good unit is available. Re-test.
- If IDM replacement does not restore signal, test or replace PCM only after confirming wiring, power, ground, and IDM are good; consult manufacturer service information and programming requirements before PCM replacement.
- Clear codes and perform a road test or crank/run cycle to confirm repair; re-scan for return of DTC.
Likely causes
- Damaged or disconnected IDM connector or wiring between coil pack and PCM
- Corroded or bent pins at PCM or IDM connector
- Failed IDM inside the coil pack or external ignition module
- Blown IGN/ECM supply fuse or poor battery/ground condition
- Short to battery or ground on the IDM signal circuit causing no valid pulse
Fault status
Status
Loss of the Ignition Diagnostic Module input to the PCM. The PCM is not receiving the expected ignition confirmation pulse from the IDM. Check wiring, connectors, power/grounds and the ignition module; replace faulty components as required.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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