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Circuit Description The Gravity (G) sensor is a vertical low-g (gravity)-acceleration sensor. By sensing vertical acceleration caused by bumps or potholes in the road, the Powertrain Control Module (PCM) can determine if the changes in crankshaft speed are due to engine misfire or are driveline induced. If the G sensor detects a rough road condition, the PCM misfire detection diagnostic will be deactivated. The G sensor at rest output should be between 2.35 - volts (+1G). During a G sensor condition the voltage output can vary between 0.5 volt (-1G) and 4.5 volts (+3G). Conditions for Setting the DTC Rough road sensor signal is less than 0.4 volt for a total for 12.5 seconds over a 25-second period of time. Action Taken When the DTC Sets - The PCM will illuminate the malfunction indicator lamp (MIL) the first time the fault is detected. - The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data. Conditions for Clearing the MIL/DTC - The PCM will turn the MIL "OFF" on the third consecutive trip cycle in which the diagnostic has been run and the fault is no longer present. - A history DTC P1392 will clear after 40 consecutive warm-up cycles occur without a fault. - DTC P1392 can be cleared by using the scan tool "Clear Info" function or by disconnecting the PCM battery feed. Diagnostic Aids Check for the following conditions: - Poor connection at PCM - Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection. - Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the G sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault. - Since the G sensor shares PCM 5 V reference and ground terminals with the MAP sensor, a damaged Manifold Absolute Pressure (MAP) harness or sensor could cause a G sensor DTC to be set. - The G sensor will give correct voltages only if it is level and mounted securely to its bracket. If DTC P1392 cannot be duplicated, the information included in the Failure Records data can be useful in determining when the DTC was last set. If it is determined that the DTC occurs intermittently, performing the DTC P1392 Diagnostic Chart may isolate the cause of the fault.
Diagnostic Test 1. Was the "On-Board Diagnostic (OBD) System Check" performed? [YES] Go to Step 2. [NO] Go to OBD System Check.(you can skip this step)
2. a. Ignition "ON", engine "OFF". b Disconnect the G sensor electrical connector. c. Observe the rough road value displayed on the scan tool. d. Is the rough road value near the specified value? [VALUES] 0.0. volts. [YES] Go to Step 4. [NO] Go to "Engine Cranks But Will Not Run".
3. a. Ignition "ON," engine "OFF." b. Review and record scan tool Failure Records data. c. Operate vehicle within Failure Records conditions as noted. d. Using a scan tool, monitor "Specific DTC" info for DTC P1392. e. Does the scan tool indicate DTC P1392 failed? [YES] Go to Step 4. [NO] Refer to Diagnostic Aids.
4. a. Disconnect the G sensor electrical connector. b. Jumper the 5 volt reference "A" circuit and the G sensor signal together at the G sensor harness connector. c. Observe the rough road value displayed on the scan tool. d. Is the rough road value near the specified value? [VALUES] 4.95 volts. [YES] Go to Step 9. [NO] Go to Step 5.
5. a. Ignition "OFF." b. Disconnect the PCM and check the 5 volt reference "A" circuit for an open or short to ground. c. If the 5 volt reference "A" circuit is open or shorted to ground, repair it as necessary. d. Was the 5 volt reference "A" circuit open or shorted to ground? [YES] Verify repair. [NO] Go to Step 6.
6. a. Check the 5 volt reference "A" circuit for a poor connection at the PCM and replace the terminal if necessary. b. Did the terminal require replacement? [YES] Verify repair. [NO] Go to Step 7.
7. a. Ignition "OFF. b. Disconnect the PCM, and check the rough road signal circuit for an open, short to ground, or short to the sensor ground circuit. c. If the G sensor signal circuit is open or shorted to ground, repair it as necessary. d. Was the rough road signal circuit open or shorted to ground? [YES] Verify repair. [NO] Go to Step 8.
8. a. Check the G sensor signal circuit for a poor connection at the PCM and replace the terminal if necessary. b. Did the terminal require replacement? [YES] Verify repair. [NO] Go to Step 10.
9. a. Replace the G Sensor. b. Is the action complete? [YES] Verify repair.
10. a. Replace the PCM. IMPORTANT: The replacement PCM must be programmed. b. Is the action complete? [YES] Verify repair.
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