P1393

DTC P1391, P1392, or P1393

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provide an overview of each diagnostic category.

DTC Descriptors

DTC P1391
- Rough Road Sensor Performance

DTC P1392
- Rough Road Sensor Circuit Low Voltage

DTC P1393
- Rough Road Sensor Circuit High Voltage

Diagnostic Fault Information






Typical Scan Tool Data






Circuit/System Description

The rough road sensor is a vertical low G-acceleration sensor. By sensing vertical acceleration caused by rough road conditions, the engine control module (ECM) can determine if the changes in crankshaft speed are due to engine misfire or are driveline induced. If the rough road sensor detects a rough road condition, the ECM misfire detection diagnostic will be de-activated. The rough road sensor at rest output should be between 2.30-2.65 volts. During a rough road condition, the voltage output can vary between 0.5-4.5 volts. The rough road sensor is a capacitive type sensor with 3 circuits:

* A 5-volt reference circuit
* A low reference circuit
* A signal circuit

The ECM provides the rough road sensor with 5 volts on the 5-volt reference circuit and a ground on the low reference circuit. Vibration to the rough road sensor from rough road conditions in the road, provides the ECM with a signal voltage from less than 1 volt to greater than 4 volts.

Conditions for Running the DTC

P1391
* The engine has been running for greater than 10 seconds.
* The vehicle speed is less than 5 km/h (3.1 mph).
OR
* The engine has been running for greater than 10 seconds.
* The vehicle speed is between 30-70 km/h (19-43 mph).
* The DTC runs continuously when the above conditions are met.

P1392 and P1393
* The engine has been running for greater than 10 seconds.
* The DTCs run continuously when the above condition is met.

Conditions for Setting the DTC

P1391

The ECM detects that the rough road sensor output is not within range.

P1392

The ECM detects that the rough road sensor voltage is less than 0.1 volt.

P1393

The ECM detects that the rough road sensor output is greater than 4.9 volts.

Action Taken When the DTC Sets

DTC P1391, P1392, and P1393 are Type C DTCs.

Conditions for Clearing the DTC

DTC P1391, P1392, and P1393 are Type C DTCs.

Diagnostic Aids

* If a shared 5-volt reference circuit is shorted to ground or shorted to a voltage, other 5-volt reference circuits may be affected.
* The scan tool 5 volt reference parameter should display between 4.8-5.2 volts.

Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. Verify DTCs P0641 or P0651 are not set.

• If either DTC is set, Refer to DTC P0641 or P0651. P0641 P0651

2. Start the engine, observe the rough road sensor voltage parameter. The reading should be between 1.1-3.7 volts.
3. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records List.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector of the rough road sensor.
2. Ignition ON, verify that the rough road sensor parameter is less than 0.1 volt.

• If greater than 0.1 volt, test the signal circuit of the rough road sensor for a short to voltage. If the circuit/connections test normal, replace the ECM.

3. Ignition ON, test for less than 0.2 volt between the low reference circuit and ground.

• If greater than 0.2 volt, test the low reference circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.

4. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit and ground.

• If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.

5. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit and ground.

Important: The 5-volt reference circuits are internally and externally connected at the ECM. Other component DTCs may be set. If other DTCs are set, review the electrical schematic and diagnose the applicable circuits and components.

• If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuit/connections test normal, replace the ECM.

• If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.

6. Ignition ON, install a 3A fused jumper wire between the signal circuit and the 5-volt reference circuit. Verify that the rough road sensor parameter is greater than 4.8 volts.

• If less than 4.8 volts, test the signal circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.

7. If all circuits/connections test normal, replace the rough road sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Rough Road Sensor Replacement
* Programming and Relearning for ECM setup, and programming Programming and Relearning