Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 26 other vehicles, including the 1999 Mercury Tracer, 1999 Mercury Sable, 1999 Mercury Mystique, 1999 Mercury Mountaineer, and 1999 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test only when directed here by a driveability symptom. This test is only intended to diagnose:

Wiring harness circuits (SIL).
SIL bulb and SIL circuit fuse.
Powertrain Control Module (PCM).
1. 1) Check SIL Operation Inspect SIL while driving vehicle. SIL should turn on when optimum-shift RPM for each gear is reached. SIL should turn off after shift is complete or while in top gear. If SIL is always illuminated, go to step 7). If SIL does not illuminate, go to next step.
2. 2) Check METER Fuse Cycle ignition on and off, then back on. If Malfunction Indicator Light (MIL) illuminates with ignition on, go to step 5). If MIL indicator does not illuminate with ignition on, remove and inspect METER fuse from central junction box. Central junction box is located on left side of instrument panel, left of steering column. If fuse is okay, reinstall fuse and go to next step. If fuse is blown, replace fuse. Cycle ignition on and off and recheck fuse. If fuse blows again, check for short to ground in Black/Yellow wire between fuse and instrument cluster. Repair wiring as necessary. Recheck SIL operation.
3. 3) Check For Voltage To METER Fuse
  
  Turn ignition on. Using a DVOM, measure voltage between chassis ground and input (power supply) side of METER fuse. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, check for open or high resistance in power supply circuit to METER fuse.
4. 4) Check For Open In VPWR Circuit To Instrument Cluster
  
  Turn ignition off. Disconnect instrument cluster White 10-pin connector C254. Turn ignition on. On Coupe models, measure voltage between chassis ground and instrument cluster harness connector C254 terminal No. 6 (Black/Yellow wire). On Sedan and Wagon models, measure voltage between chassis ground and instrument cluster harness connector C254 terminal No. 10 (Black/Yellow wire). On all models, if voltage is 10.5 volts or less, repair open in Black/Yellow wire between METER fuse and instrument cluster. If voltage is more than 10.5 volts, check for burned SIL bulb or faulty instrument cluster. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
5. 5) Check SIL Circuit For Open
  
  Turn ignition off. Disconnect instrument cluster White 10-pin connector C254 (Coupe) or Black 12-pin connector C252 (Sedan and Wagon). On all models, disconnect PCM 104-pin connector. PCM is located under center of instrument panel. Inspect connector for damage and repair as necessary. On Coupe models, measure resistance of Pink wire between instrument cluster harness connector C254 terminal No. 7 and PCM connector pin No. 72. On Sedan and Wagon models, measure resistance of Pink wire between instrument cluster harness connector C252 terminal No. 2 and PCM connector pin No. 72. On all models, if resistance is 5 ohms or more, repair open in Pink wire between PCM and instrument cluster. If resistance is less than 5 ohms, go to next step.
6. 6) Attempt To Illuminate Shift Indicator Light
  
  Turn ignition off. Reconnect instrument cluster connector. Connect a jumper wire between chassis ground and PCM connector pin No. 72 (Pink wire). Turn ignition on. If SIL illuminates, replace PCM. If SIL does not illuminate, check for burned SIL bulb or faulty instrument cluster. See appropriate INSTRUMENT PANEL article in ACCESSORIES & EQUIPMENT.
7. 7) Check Instrument Cluster For Short To Ground
  
  Turn ignition off. Disconnect instrument cluster White 10-pin connector C254 (Coupe) or Black 12-pin connector C252 (Sedan and Wagon). Turn ignition on. If SIL remains illuminated, repair short to ground in instrument cluster or replace instrument cluster. If SIL does not remain illuminated, go to next step.
8. 8) Check SIL Circuit For Short To Ground
  
  Turn ignition off. Ensure instrument cluster connector C254 (Coupe) or C252 (Sedan and Wagon) is still disconnected. Disconnect PCM 104-pin connector. PCM is located under center of instrument panel. Inspect connector for damage and repair as necessary. Using a DVOM, measure resistance between chassis ground and PCM connector pin No. 72 (Pink wire). If resistance is 10 k/ohms or less, repair short to ground in Pink wire between PCM and instrument cluster. If resistance is more than 10 k/ohms, replace PCM.