• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
5-Volt Reference | P1392 | P1392 | P1393 | P1391 |
Rough Road Sensor Signal | P1392 | P1392 | P1393 | P1391 |
Low Reference | -- | P1391 | -- | P1391 |
Circuit | Short to Ground | Open | Short to Voltage |
---|---|---|---|
Operating Conditions: Engine operating in Closed Loop. Parameter Normal Range: 1.1-3.7 Volts. | |||
5-Volt Reference | 0.0 Volts | 0.0 Volts | 5.0 Volts¹ |
Rough Road Sensor Signal | 0.0 Volts | 0.0 Volts | 5.0 Volts¹ |
Low Reference | -- | 0.0 Volts | 5.0 Volts¹ |
¹ Internal ECM or sensor damage may occur if the circuit is shorted to B+ |
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 2.3-2.65 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 more than 4 volts.
• | The engine has been running for more than 10 seconds. |
• | The vehicle speed is less than 5 km/h (3.1 mph). |
OR |
• | The engine has been running for more 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. |
• | The engine has been running for more than 10 seconds. |
• | The DTCs run continuously when the above condition is met. |
The ECM detects that the rough road sensor output is not within range.
The ECM detects that the rough road sensor voltage is less than 0.1 volt.
The ECM detects that the rough road sensor output is more than 4.9 volts.
DTC P1391, P1392, and P1393 are Type C DTCs.
DTC P1391, P1392, and P1393 are Type C DTCs.
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
⇒ | 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. |
Important: The test lamp is used to load the circuit and may not illuminate.
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 of the rough road sensor 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 of the rough road sensor for a short to voltage. If the circuit/connections test normal, replace the ECM. |
⇒ | If greater than 0.2 volt, test the low reference circuit of the rough road sensor for a short to voltage. If the circuit/connections test normal, replace the ECM. |
⇒ | If greater than 5 ohms, test the low reference circuit of the rough road sensor for an open/high resistance. If the circuit/connections test normal, replace the ECM. |
⇒ | If less than 4.8 volts, test the signal circuit of the rough road sensor for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for ECM replacement, setup, and programming |