Diagnostic Aids

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

• Wiring harness circuits (SIL).
• Top gear switch.
• SIL dimmer relay.
• SIL bulb and SIL circuit fuse.
• Powertrain Control Module (PCM).

1. Step 1) Check SIL Operation  Inspect SIL while driving vehicle. SIL should turn on when optimum-shift RPM for each gear is reached. Light should be off in top gear. If SIL light is always on, check for short to ground in SIL circuit. If light is always off, check for open in SIL circuit. If light is always on, go to step 4). If light is not always on, go to next step.
2. Step 2) Check SIL Circuit Fuse  Turn ignition off. Remove and inspect SIL fuse. If fuse is okay, go to next step. Replace fuse if blown. If fuse blows again, repair short to ground between fuse and SIL bulb. Check SIL operation.
3. Step 3) Check SIL Bulb  Turn ignition off. Remove and inspect SIL bulb. If bulb is burned out, replace bulb and check SIL operation. If bulb is okay, go to step 5).
4. Step 4) Check SIL Circuit For Short To Ground  Turn ignition off. Put transmission in high gear. Disconnect PCM wiring harness connector. Inspect pins for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between test pins No. 53 and 60 at breakout box. If resistance is 10,000 ohms or less, repair short between top gear switch and PCM. Reconnect all components, and repeat QUICK TEST. If resistance is more than 10,000 ohms, replace PCM and repeat QUICK TEST .
5. Step 5) Check For Voltage To SIL Socket  Turn ignition off. Remove SIL bulb. Place transmission in any gear except top gear. Turn ignition on. Measure voltage between power contact at SIL socket and chassis ground. If voltage is more than 10.5 volts, go to step 7). If voltage is 10.5 volts or less, connect SIL bulb and go to next step.
6. Step 6) Check Operation Of Top Gear Switch  Top gear switch is normally closed and should only be open when vehicle is shifted into top gear. Turn ignition off. Disconnect top gear switch. Place transmission in any gear except top gear. Measure resistance between top gear switch terminals. If resistance is less than 5 ohms, repair open in IGNITION RUN circuit to SIL bulb socket. Check SIL operation. If resistance is 5 ohms or more, replace top gear switch. Check SIL operation.
7. Step 7) Check Continuity Of SIL Circuit  Turn ignition off. Remove SIL bulb. Disconnect PCM wiring harness connector. Inspect pins for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between test pin No. 72 and SIL power contact at SIL bulb socket. If resistance is less than 5 ohms, replace PCM. Check SIL operation. If resistance is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and check SIL operation.