Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Explorer and 1995 Ford Aerostar. However, it is still accessible from the selected car via links, so may be relevant.

The IDM is an input signal to the PCM that verifies spark plug fire based on ignition coil primary discharge. IDM signal consists of a single pulse for each engine RPM. No IDM pulse indicates secondary ignition misfire.

Perform this test when directed by QUICK TEST. This test is only intended to diagnose EEC-IV portion of ignition system. For additional information on ignition system and component testing, see SYSTEM/COMPONENT TESTS - EEC-IV (4.0L) article in the ENGINE PERFORMANCE section. To prevent replacing good components, be aware following non-EEC related areas may be at fault:

Ignition Control Module (ICM).
Ignition coil packs.
Spark plugs and/or wires.
Crankshaft Position (CKP) sensor.
Secondary ignition short to ground. This test is intended to diagnose:
IDM Wiring harness circuits.
Powertrain Control Module (PCM).

Fig 1: IDM Circuit Schematic (4.0L)

1) Continuous Memory Code 211: Erratic Ignition Code 211 indicates 2 successive erratic Profile Ignition Pick-Up (PIP) pulses occurred. Possible causes for this fault are:

Loose wires or connectors.
Secondary ignition short to ground.
On-board transmitter equipment (2-way radio).

Repair any problems found, and repeat QUICK TEST. If problem is not found, go to step 4). If vehicle does not start, go to CIRCUIT TEST AC.

2) Code 226: IDM Circuit Failure Code 226 indicates PCM did not receive IDM signal from ICM in KOEO SELF-TEST. Possible causes for this problem are:

Open or shorted IDM or IGN GND circuit wiring harness.
Faulty ICM.

If engine does not start, go to IGNITION SYSTEMS in SYSTEM/COMPONENT TESTS - EEC-IV (4.0L) article. If engine starts, go to step 4).

3) Continuous Memory Code 212: Check For Other Codes Code 212 indicates loss of IDM input signal to PCM. Possible causes for this fault are:

Open or short circuit in wiring harness.
Faulty ICM.
Faulty PCM.

Attempt to start vehicle. If vehicle does not start, go to CIRCUIT TEST AC. If vehicle starts, run engine 5-10 minutes. Repeat KOEO SELF-TEST and record codes. If Continuous Memory Code 215, 216, 217 or 232 is present, go to IGNITION SYSTEMS in appropriate SYSTEM/COMPONENT TESTS - EEC-IV (4.0L) article in the ENGINE PERFORMANCE section. If Code 212 is present, go to next step. If no codes are present, fault is intermittent. Perform wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST.

4) Check IDM Circuit Continuity Turn ignition off. Disconnect ICM. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 4 at breakout box and IDM terminal No. 2 at ICM wiring harness connector. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST. If resistance is less than 5 ohms, go to next step.

5) Check IDM Circuit For Short To Power (Except VREF) Leave PCM and ICM disconnected. Monitor circuit voltage by connecting DVOM between test pin No. 4 and test pin No. 40 or 60. To check VBAT circuit, turn ignition off. To check VPWR circuit, turn ignition on. If either voltage reading is more than 10.5 volts, repair short circuit and repeat QUICK TEST. If voltage is 10.5 volts or less, go to next step.

6) Check IDM Circuit For Short To VREF & PIP Turn ignition off. Ensure PCM and ICM are disconnected. Disconnect scan tool (if applicable). To check for short to VREF, use DVOM to measure resistance between test pins No. 4 and 26 at breakout box. To test for short to PIP, measure resistance between test pins No. 4 and 56 at breakout box. If either resistance is 10,000 ohms or less, repair short circuit and repeat QUICK TEST. If each resistance is more than 10,000 ohms, go to next step.

During this test, a short to SIG RTN (pin No. 46) may be indicated along with an actual short to PWR GND when 4-wire HO2S is connected to vehicle wiring harness.

7) Check IDM Circuit For Short To Ground Leave PCM and ICM disconnected. Measure resistance between test pin No. 4 and test pins No. 40, 46 and 60 at breakout box. If any reading is less than 10,000 ohms, repair short to ground in IDM circuit and repeat QUICK TEST. If all readings are 10,000 ohms or more, go to next step.

8) Check ICM Leave ignition off. Connect ICM to wiring harness connector. Connect PCM to breakout box. Start engine, and allow it to idle. Connect DVOM to test pins No. 4 and 16. Start engine. Observe DVOM for fault (voltage surge) while lightly tapping on ignition components to simulate road shock. Wiggle both ICM wiring harness connectors. If fault is indicated, disconnect and inspect ICM wiring harness connectors and terminals for damage. If connectors and terminals are okay, check ignition system. Proceed to the appropriate SYSTEM/COMPONENT TESTS - EEC-IV (4.0L) article in the ENGINE PERFORMANCE section. If fault is not indicated, leave DVOM connected to breakout box and go to next step.

9) Check EEC-IV Harness Ensure engine is idling at correct RPM. Wiggle, shake or bend small sections of harness, working from ICM connectors to firewall. Observe DVOM for indication of fault. Repeat process from firewall to PCM. If fault is indicated, isolate fault and repair wiring harness. Repeat QUICK TEST. If no fault is indicated, go to next step.

10) Check PCM & Harness Connectors Turn ignition off. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. If connector is damaged, repair as necessary. Clear codes, and repeat QUICK TEST. If connector is okay, go to next step.

11) Check PCM For Short To Power Turn ignition off. Disconnect ICM connectors. Connect PCM to breakout box. Measure voltage between test pin No. 4 and chassis ground. Turn ignition on. Measure voltage between test pin No. 4 and pins No. 40 and 60. If either voltage is more than 10.5 volts, replace PCM and repeat QUICK TEST. If each voltage is 10.5 volts or less, go to next step.

12) Check PCM For Short To Ground Turn ignition off. Leave ICM connectors disconnected. Ensure PCM is connected to breakout box. Measure resistance between test pin No. 4 and pins No. 16, 20, 40, 46 and 60. If each resistance is more than 10,000 ohms, EEC system is okay. Check ignition system. See SYSTEM/COMPONENT TESTS - EEC-IV (4.0L) article in the ENGINE PERFORMANCE section. If any resistance is 10,000 ohms or less, replace PCM and repeat QUICK TEST.