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Speedometer Inoperative

  1. Vehicle speed sensor signal is sent to PCM. PCM buffers signal and feeds a pulse train to IPC of 4000 pulses per mile through Red/White wire circuit. IPC supplies system voltage to Red/White 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.
  2. Enter self-diagnostics. See ENTERING SELF-DIAGNOSTICS under SELF-DIAGNOSTICS. If code E024 is set, repair this problem first. See CODE E024 in appropriate BASIC TESTING article in ENGINE PERFORMANCE Section. 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).
  3. 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 MPH, compare data value to speedometer display. If speedometer is inoperative, replace IPC. If speedometer is about 1.07 times more than ID60 value, see IPC MALFUNCTION SYMPTOMS under SELF-DIAGNOSTICS.
  4. 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 Red/White wire is near secondary ignition wires, and move it as required.
  5. Using DVOM with negative probe connected to ground, backprobe IPC 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.
  6. If voltage is fixed at 12 volts, disconnect PCM Black connector No. C2. See Figure. PCM is mounted to right kick panel. Connect jumper wire between PCM harness connector C2 terminal B11 and ground. Using DVOM connected to ground, backprobe positive probe to IPC connector terminal C4. If DVOM reading is zero volts, replace PCM. If DVOM reading is system voltage, repair open in Red/White wire circuit between IPC and PCM.
  7. If voltage is fixed at zero volts, disconnect PCM connector C2. Using DVOM with negative probe connected to ground, backprobe IPC connector terminal C4. If DVOM reading is now system voltage, replace PCM. If DVOM reading is zero volts, turn ignition off. Disconnect IPC connector. Ensure PCM connector C2 is still disconnected.
  8. Using DVOM, measure resistance between IPC terminal C4 and ground. See Figure. If resistance is less than 1000 ohms, repair short to ground in Red/White wire. If resistance is 1000 ohms or more, check connections at IPC terminal C4. If connections are good, replace IPC.
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