The P1231 diagnostic trouble code is a manufacturer-specific powertrain code. Its exact definition depends heavily on the vehicle make, pointing to a fuel pump relay issue, a throttle position sensor fault, or an injector circuit malfunction.
Because this code targets entirely different systems across manufacturers, the exact vehicle application must be verified before diagnosis. The code alone does not prove a specific component has failed without proper testing.
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Key Takeaways
- P1231 is a manufacturer-specific powertrain code with differing definitions depending on the vehicle make.
- On Ford, Lincoln, and Toyota applications, it indicates a High Speed Fuel Pump Relay Activated or Fuel Pump Secondary Circuit fault.
- On Saab applications, it points to a Throttle Position Sensor 1 and 2 Circuit Sum Out of Range fault.
- On GM and Chevrolet applications, it indicates an Injector Circuit Cylinder 4 Intermittent fault.
- Diagnosis requires verifying the exact factory definition and testing the relevant fuel pump, throttle, or injector circuit.
P1231 Code Description and Implications
The P1231 code indicates that a control module has detected a specific fault within the fuel delivery, throttle control, or fuel injection systems. Because it is a manufacturer-specific code, the exact monitored component varies significantly by brand.
Some Ford, Lincoln, and Toyota applications: P1231 indicates a High Speed Fuel Pump Relay Activated or Fuel Pump Secondary Circuit Low fault. The PCM detects an issue with the high-speed fuel pump relay control circuit.
Certain Saab applications: The code indicates a Throttle Position Sensor 1 and 2 Circuit Sum Out of Range fault. The ECM detects that the combined voltage signals from the dual throttle position sensors fall outside the expected parameters.
Some GM and Chevrolet applications: P1231 indicates an Injector Circuit Cylinder 4 Intermittent fault. The control module detects an erratic signal or connection issue in the fuel injector circuit for cylinder 4.
Common Causes of the P1231 Code
Because P1231 applies to different systems across different brands, the root cause depends on the verified vehicle application.
Ford, Lincoln, and Toyota Causes: A faulty high-speed fuel pump relay, damaged wiring or poor electrical connections at the relay or PCM, or a failing fuel pump assembly drawing excessive current.
Saab Causes: A failing electronic throttle body assembly, damaged wiring or poor electrical connections at the throttle position sensor connector, or carbon buildup restricting throttle plate movement.
GM and Chevrolet Causes: A faulty fuel injector for cylinder 4, damaged wiring harness, poor electrical connections, or an internal ECM driver issue affecting the injector control circuit.
Symptoms Associated With P1231
When the control module detects a critical system fault, it illuminates a warning light and may alter vehicle operation.
Warning Lights: The Check Engine Light will illuminate. On some applications, a reduced power or limp mode warning may also appear.
Drivability: On Ford and Toyota applications, the engine may stall, crank without starting, or experience fuel starvation under load. On Saab applications, rough idling, hesitation, or reduced throttle response may occur. On GM applications, a cylinder 4 misfire is likely.
Diagnosing the P1231 Trouble Code
Accurate diagnosis begins by verifying the exact vehicle application and reviewing manufacturer-specific service information.
For Ford, Lincoln, and Toyota applications: Inspect the wiring harness and connectors at the high-speed fuel pump relay. Verify the relay control signal from the PCM and test the relay operation. Check fuel pressure under load.
For Saab applications: Inspect the wiring harness and connectors at the electronic throttle body. Verify the dual throttle position sensor signals using a scan tool or oscilloscope to ensure they correlate smoothly and sum correctly.
For GM and Chevrolet applications: Inspect the wiring harness and connectors for the cylinder 4 fuel injector. Test the injector resistance and verify the control signal using a noid light or oscilloscope.
Repairing the P1231 Issue
Repairs must follow the confirmed root cause identified during diagnosis.
Fuel Pump Relay Repairs: If the high-speed fuel pump relay fails testing, replace the relay. Repair any damaged wiring or corroded connectors in the secondary fuel pump circuit.
Throttle Body Repairs: If the electronic throttle body or internal position sensors fail electrical testing, replace the throttle body assembly. Clean carbon deposits and perform the required throttle adaptation or relearn procedure.
Injector Circuit Repairs: If the cylinder 4 fuel injector fails testing, replace the injector. Repair any damaged wiring in the injector circuit and verify proper spray pattern and fuel delivery.
Cost Considerations for P1231 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Replacing an external fuel pump relay or a single fuel injector involves minimal to moderate labor. However, replacing an electronic throttle body or diagnosing complex secondary fuel pump circuits requires additional diagnostic time and potential relearn procedures.
Prevention Strategies for Future Occurrences
Ensuring electrical connectors and relay mounts are kept clean and secure helps prevent moisture intrusion and poor electrical connections in the fuel pump and injector circuits.
Keeping the throttle body clean and using high-quality fuel helps prevent carbon buildup that can restrict throttle plate movement and affect position sensor readings on applicable vehicles.
Troubleshooting Tips and Best Practices
Follow these practices to avoid misdiagnosis and ensure accurate repairs.
Do not assume the PCM is dead: A failed relay, broken wire, or corroded connector is a much more frequent cause of a fuel pump secondary circuit fault. Always verify circuit integrity before considering module replacement.
Check for related codes: Look for accompanying fuel pressure codes on Ford applications, or specific misfire codes on GM applications, which might help pinpoint the exact affected circuit.
Verify your definition: When researching this fault code, always confirm whether your specific vehicle uses the fuel pump relay, throttle position sensor, or injector circuit definition before ordering parts.
More OBD-II Codes
| P1228 | P1227 | P1226 | P1225 |
| P1224 | P1223 | P1234 | P1237 |
| P1240 | P1243 | P1244 | P1245 |
| P1250 | P1286 | P1287 | P1288 |
| P1290 | P1291 | P1292 | P1293 |
| P1294 | P1295 | P1296 | P1297 |
Frequently Asked Questions
Is P1231 a generic or manufacturer-specific code?
No. P1231 is a manufacturer-specific powertrain code. Its definition varies significantly by brand, indicating a fuel pump relay fault, a throttle position sensor issue, or an injector circuit malfunction.
Can I drive my vehicle with a P1231 code?
The vehicle may remain drivable, but a fuel pump relay fault can cause stalling or a no-start condition, while a throttle sensor fault can cause erratic acceleration and reduced power.
Will disconnecting the battery clear the P1231 code?
Disconnecting the battery might temporarily clear the code. However, it does not repair the underlying failed relay, damaged wiring, or faulty sensor, and the code will return upon the next monitor cycle.
Can a dirty throttle body cause a P1231 code?
Yes. On Saab applications where P1231 indicates a throttle position sensor sum out of range fault, severe carbon buildup can restrict the throttle plate and cause the sensor signals to fall out of expected parameters.
Does P1231 affect the transmission?
No. The P1231 code relates strictly to the engine fuel delivery system, electronic throttle body, or fuel injector circuits. It does not directly affect the automatic or manual transmission operation.
What Should You Do About the P1231 Code?
When a P1231 code appears, confirm the exact factory definition for your specific vehicle make and model. Because this code targets entirely different fuel, throttle, and injection systems depending on the manufacturer, applying the wrong diagnostic path will lead to misdiagnosis.
Follow the applicable manufacturer diagnostic procedure to test the relevant system and components. Once the root cause is confirmed, complete the necessary electrical repairs, component replacements, or adaptations before returning the vehicle to normal service.
