DTC P1391
Diagnostic Instructions
DTC Descriptor
DTC P1391: Rough Road Sensor Performance
Circuit/System Description
The engine control module (ECM) identifies engine misfire by detecting variations in crankshaft speed. Crankshaft speed variations can also occur when a vehicle is operating over a rough road. The ECM receives a rough road signal by a rough road sensor or an electronic brake control module (EBCM), if equipped with the antilock brake system (ABS). The ABS can detect if the vehicle is on the rough surface based on wheel acceleration/deceleration data supplied by each wheel speed sensor. This information is sent to the ECM by the EBCM through the rough road signal circuit. For vehicles without ABS, the ECM receives a rough road signal from a wheel speed sensor located at the front left wheel. The ECM can determine if the vehicle is on a rough road surface based on the signal from the wheel speed sensor.
Conditions for Running the DTC
• | The vehicle speed is between 5-100 km/h (3.1-62.1 mph). |
• | The DTC runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The ECM detects that the change in rough road wheel speed sensor signal is less than 2 km/h (1.2 mph) while the change in vehicle speed is greater than 5 km/h (3.1 mph).
Action Taken When the DTC Sets
DTC P1391 is a Type C DTC.
Conditions for Clearing the DTC
DTC P1391 is a Type C DTC.
Reference Information
Schematic Reference
Engine Controls Schematics : Siemens ECM - LPG with LCP → Siemens ECM - Gas without FX3 or LCP → Delphi ECM - FX3
Connector End View Reference
Component Connector End Views
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information.
Circuit/System Verification
- Observe the DTC information with a scan tool. DTC P1391 should not set.
- 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
- Ignition OFF, disconnect the harness connector at the B171 Rough Road Sensor.
- Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 2 and ground.
⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary. |
- Ignition ON, test for 0.2-0.8 V between the signal circuit terminal 1 and ground.
⇒ | 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 K20 ECM. |
⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM. |
- If all circuits test normal, replace the B171 Rough Road Sensor.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
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