Damaged, chafed, or corroded wiring in the IDM circuit between the ignition module and PCM; Failed ignition control module or coil driver not producing the IDM feedback signal; Loose or corroded ground connection at the ignition module or engine block; Faulty crankshaft position sensor or camshaft position sensor disrupting ignition timing reference; PCM internal fault on the IDM input circuit, often after water intrusion or voltage spikes; Aftermarket ignition components or poor-quality coils that do not generate a clean IDM signal; Connector pins backed out or spread at the ignition module or PCM harness

DTC codes / Ford codes / P1351

P1351 · FordIgnition Diagnostic Monitor Circuit Input Fault

Q: What does code P1351 mean?

Ignition Diagnostic Monitor Circuit Input Fault. P1351 on a Ford means the powertrain control module (PCM) is not receiving a valid signal on the Ignition Diagnostic Monitor (IDM) circuit, which is the feedback line from the ignition control module or coil driver. The PCM uses this input to confirm that each ignition event actually occurred, so when the signal is missing, erratic, or out of expected range, it stores this fault and may default to a limp ignition strategy.

P1351 on a Ford means the powertrain control module (PCM) is not receiving a valid signal on the Ignition Diagnostic Monitor (IDM) circuit, which is the feedback line from the ignition control module or coil driver. The PCM uses this input to confirm that each ignition event actually occurred, so when the signal is missing, erratic, or out of expected range, it stores this fault and may default to a limp ignition strategy.

SystemPowertrain

Code typeFord specific

SeverityMedium

Fix difficultyProfessional

AreaIgnition system and misfire

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Engine misfire or rough running, especially under load or at higher rpm
Hard starting or a crank-no-start condition in more severe cases
Reduced engine power or limp mode triggered by the PCM
Poor fuel economy or increased emissions due to incomplete combustion
Intermittent stalling that may clear after the engine warms up

Common causes, most likely first

Damaged, chafed, or corroded wiring in the IDM circuit between the ignition module and PCM
Failed ignition control module or coil driver not producing the IDM feedback signal
Loose or corroded ground connection at the ignition module or engine block
Faulty crankshaft position sensor or camshaft position sensor disrupting ignition timing reference
PCM internal fault on the IDM input circuit, often after water intrusion or voltage spikes
Aftermarket ignition components or poor-quality coils that do not generate a clean IDM signal
Connector pins backed out or spread at the ignition module or PCM harness

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm P1351 is the only ignition-related fault
Inspect the IDM circuit wiring and connectors for chafing, corrosion, or loose pins, repairing as needed
Check and clean the ignition module and engine block ground connections, then retest
Measure the IDM signal with an oscilloscope or logic probe at the PCM while cranking to verify presence and shape
Test or swap the ignition control module or coil driver with a known-good unit to isolate the fault
Verify crankshaft and camshaft sensor signals are clean and in sync, replacing if erratic
If all external circuits and components test good, diagnose the PCM IDM input circuit or replace the PCM as a last step

What the IDM circuit really tells the PCM

A missing IDM signal does not always mean the ignition module is dead; a bad ground or a chafed wire in the harness is just as common and far cheaper to fix.
Aftermarket coils and ignition modules frequently produce an IDM waveform the PCM rejects, so this code can appear right after a tune-up or performance ignition install.
The IDM circuit is a feedback line, not a control line, so the engine may still run and start normally while the code is stored, which leads many drivers to ignore it until a misfire develops.
Water intrusion into the PCM connector or ignition module housing can corrode the IDM pin and set this code without any visible driveability problem.
A failing crankshaft position sensor can disrupt the ignition event timing enough that the PCM flags the IDM input as invalid, even though the sensor itself has not yet set its own code.

Can I keep driving with P1351?

You can usually drive short distances to a repair shop if the engine runs smoothly and the light is steady, but avoid heavy throttle, towing, or long trips until the fault is diagnosed. If the engine misfires, stalls, or enters limp mode, stop driving and arrange a tow to prevent catalytic converter damage.

Tools that help

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