Circuit Description
The rough road (G) sensor is a vertical low G-acceleration sensor. By sensing vertical acceleration caused by bumps or potholes in the road, the powertrain control module (PCM) can determine if the change in crankshaft speed are due to engine misfire or driveline induced. If the rough road sensor detects a rough road condition , the PCM misfire detection diagnostic will be disabled. The rough road sensor at rest output is +1G (2.5 volts). During a rough road condition the voltage output can vary between -1G (0.5 volts) to +3G (4.5 volts).
Conditions for Running the DTC
| • | The engine is running. |
| • | No vehicle speed |
Conditions for Setting the DTC
The rough road sensor signal is less than 0.1 volts for a total of 3 seconds.
Action Taken When the DTC Sets
| • | The powertrain control module (PCM) stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records. |
Conditions for Clearing the DTC
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Use a scan tool in order to clear the DTC. |
Diagnostic Aids
Inspect for the following conditions:
| • | A poor electrical connection at the PCM -- Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | A damaged harness -- Inspect the wiring harness for damage. If the harness appears to be OK, observe the rough road display on the scan tool while moving connectors and wiring harness related to the sensor. A change in the display will indicate the location of the fault. |
If the Rough Road sensor ground circuit is open, this will cause the sensor output voltage to go high, from 4.1 to 4.2 volts, but the voltage is not high enough to set DTC P1393. DTC P1393 will set for this open sensor ground circuit after several minutes of driving.
Reviewing the Failure Records vehicle kilometers (miles) since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Did DTC P1635 fail this ignition? | -- | ||
3 |
Is the rough road value near the specified value? | 0 V | ||
Does the scan tool indicate DTC P1392 failed? | -- | Go to Diagnostic Aids | ||
5 |
Is the rough road sensor value near the specified value? | 4.95 V | ||
6 |
Is the rough road sensor value near the specified value? | 4.95 V | ||
7 |
Was a problem found? | -- | ||
8 |
Was a problem found? | -- | ||
9 |
Was a problem found? | -- | ||
10 |
Was a problem found | -- | ||
11 | Replace the rough road sensor. Is the action complete? | -- | -- | |
12 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |
13 |
Does the scan tool indicate that this test ran and passed? | -- | ||
14 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
