Diagnostic Aids
- 1) DTC 1298 & 1668
DTC 1298 (1995 models) and DTC 1668 (1995-96 models) indicate that a communication error has occurred between PCM and IDM. DTC 1668 indicates a PCM/IDM communication error. Possible causes for this DTC are:- Open fuse.
- IDM relay.
- Open or short in IDM enable circuit.
- Open or short in EF circuit.
- Open or short in FDCS circuit.
- IDM powering circuits.
- Faulty Powertrain Control Module (PCM).
Repeat KOEO SELF-TEST , retrieve Continuous Memory DTCs and perform the following:
- If DTC 1668 is present, go to next step.
- If DTCs P1667 and P1663 are present with or without DTC P1668, go to step 6).
- If DTC 1298 is present with DTC 1668, replace IDM.
- If DTC 1667 is present with DTC 1668, go to TEST V, step 1).
- If DTC P1663 is present with DTC 1668, go to TEST T, step 1).
- If DTC P1662 is present with DTC 1668, go to TEST W, step 1).
- 2) Check Gray/White Wire For Open
Install breakout box. Leave PCM disconnected. Disconnect IDM harness connector. Measure resistance of Gray/White wire between breakout box test Pin No. 48 and IDM harness connector terminal No. 4. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Gray/White wire. Reconnect connectors. Clear DTCs and repeat QUICK TEST . - 3) Check Gray/White Wire For Short To Ground
Measure resistance of Gray/White wire between IDM and negative battery terminal. If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in Gray/White wire. Reconnect connectors. Clear DTCs and repeat QUICK TEST . - 4) Check Gray/White Wire For Short To Power
Turn ignition on. Measure voltage between breakout box Test Pin No. 48 and negative battery terminal. If voltage is present, repair short to power in Gray/White wire. Reconnect connectors. Clear DTCs and repeat QUICK TEST . If voltage is not present, go to next step. - 5) Check Gray/Red Wire For Continuity
Measure resistance of Gray/Red wire between breakout box test Pin No. 91 and IDM harness connector terminal No. 2. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Gray/Red wire. Reconnect connectors. Clear DTCs and repeat QUICK TEST . - 6) Check IDM Power Supply
Ensure PCM is connected and IDM is disconnected. Turn ignition on. Measure voltage between IDM harness connector terminal No. 14 (Dark Green/Light Green wire) and negative battery terminal. If battery voltage is present, go to next step. If battery voltage is not present, go to TEST W, step 6). - 7) Check IDM Ground
Turn ignition off. Measure resistance between IDM harness connector terminal No. 26 (Black/White wire) and negative battery terminal. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Black/White wire between IDM and chassis ground. Reconnect connectors. Clear DTCs and repeat QUICK TEST . - 8) Measure Frequency On EF Circuit
Connect PCM to breakout box. Ensure IDM is connected to harness. Connect NGS Tester as follows:- Install NGS tester to DLC.
- Connect test probe between NGS common and breakout box test Pin No. 77 (ground).
- Connect second test probe between NGS signal and breakout box test Pin No. 48 (EF line).
- Select VEHICLE and ENGINE.
- Select DIGITAL MEASUREMENT SYSTEM.
- Change voltage level to 4-volt DC.
- Press link button to choose a PID.
- Select PID/DATA MONITOR & RECORD.
- Select RPM PID.
- Press START.
Turn ignition on. Measure frequency at 1000, 2000 and 3000 RPM. Refer to ENGINE SPEED-TO-FREQUENCY SIGNAL table. If all frequencies are as specified for each RPM value, replace PCM. Reconnect connectors. Clear DTCs and repeat QUICK TEST . If any frequency value is not as specified for that RPM value, replace IDM. Reconnect connectors. Clear DTCs and repeat QUICK TEST .
ENGINE SPEED-TO-FREQUENCY SIGNALEngine Speed - RPM Frequency - Hz. 1000 66 2000 133 3000 200