P1393
DTC P1391, P1392, or P1393
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides 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.
Reference Information
Schematic Reference
Engine Controls Schematics (MR140 w/o Throttle Actuator Control) (Electrical Diagrams)Engine Controls Schematics (MT34 w/Throttle Actuator Control) (Electrical Diagrams)Engine Controls Schematics (Hatchback) (Electrical Diagrams)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning)for scan tool information
Circuit/System Verification
1. Ignition ON, observe the DTC information with a scan tool. Verify DTCs P0641 or P0651 are not set.
• If any DTC is set, refer to DTC P0641 or P0651 (P0641).
2. Engine running, observe the scan tool rough road sensor voltage parameter. The reading should be between 1.1-3.7 volts.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the rough road sensor.
2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit and ground.
* Hatchback low reference circuit terminal A
* Notchback low reference circuit terminal C
• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit and ground.
* Hatchback 5 volt reference circuit terminal C
* Notchback 5 volt reference circuit terminal A
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 the specified range, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the ECM.
• If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
4. Ignition ON, verify the scan tool rough road sensor parameter is less than 0.1 volt.
• If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
5. Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit. Verify the scan tool rough road sensor parameter is greater than 4.8 volts.
* Hatchback 5 volt reference circuit terminal C
* Notchback 5 volt reference circuit terminal A
• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
6. If all circuits test normal, test or replace the rough road sensor.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Rough Road Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for ECM replacement, setup, and programming