Speedometer Inoperative/Inaccurate
- Vehicle speed sensor signal is sent to PCM. PCM buffers signal and feeds a pulse train to IPC of 4000 pulses per mile through Brown wire circuit. IPC supplies system voltage to Brown wire circuit, and PCM pulses this circuit to ground to transmit speed signal. IPC uses this pulse data value to calculate and display vehicle speed.
- Enter self-diagnostics. See ENTERING SELF-DIAGNOSTICS under SELF-DIAGNOSTICS. If Code E024 is set, repair this problem first. See CODE E024 in TESTS W/CODES
- Eldorado or TESTS W/CODES
- 4.6L - Seville article in the ENGINE PERFORMANCE section.NOTE: If Code E024 is not set, raise drive wheels and properly support vehicle. Start engine and re-enter self-diagnostics if necessary.
- Select IPC data parameter ID60 (vehicle speed). Put shifter in Drive position, and allow wheels to rotate at engine idle. If parameter ID60 data value is zero, go to step 5). If parameter ID60 data value is greater than zero, compare data value to speedometer display. If speedometer is inoperative, replace IPC. See INSTRUMENT PANEL CLUSTER under REMOVAL & INSTALLATION. If speedometer is about 1.07 times more than ID60 value, see IPC MALFUNCTION SYMPTOMS under SELF-DIAGNOSTICS.
- If one or both readings are erratic and speedometer display is fluctuating while ID60 is constant speed, replace IPC. If ID60 is fluctuating with speedometer display, check terminal connections and wiring circuit for intermittent problem. Check if Brown wire is near secondary ignition wires, and move it as required.
- Using DVOM with negative probe connected to ground, backprobe IPC White connector terminal C4 while wheels are turning. See Figure. If voltage varies with speed, check connections at IPC terminal C4. If connections are good, replace IPC. See INSTRUMENT PANEL CLUSTER under REMOVAL & INSTALLATION.
- If voltage is fixed at zero volts, go to next step. If voltage is fixed at 12 volts, turn engine off. Turn ignition on and disconnect PCM connector C2. See Fig 1. PCM is mounted to right kick panel. Using DVOM connected to ground, measure voltage at PCM connector C1 terminal 1B11. If battery voltage is present, replace PCM. If zero voltage is present, repair open in Brown wire circuit between IPC and PCM.
- Turn engine off. Turn ignition on. Disconnect PCM connector C2. Using DVOM with negative probe connected to ground, backprobe IPC connector terminal C4. See Figure. If DVOM reading is now system voltage, replace PCM. If DVOM reading is zero volts, turn ignition off. Disconnect IPC connector. Ensure PCM connector is still disconnected.
- Using DVOM, measure resistance between IPC connector terminal C4 and ground. See Figure. If resistance is less than 1000 ohms, repair short to ground in Brown wire. If resistance is 1000 ohms or more, check connections at IPC terminal C4. If connections are good, replace IPC. See INSTRUMENT PANEL CLUSTER under REMOVAL & INSTALLATION.