Fuel Pump Secondary Circuit Low Voltage
The P0231 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the fuel pump secondary circuit. This circuit typically includes the fuel pump relay, wiring, and the fuel pump itself. A low voltage reading suggests excessive resistance, a short to ground, or a failing fuel pump. This can lead to insufficient fuel pressure, causing drivability issues.
1. Most Common Causes
- Faulty fuel pump relay with burned or pitted contacts
- Secondary circuit wiring with excessive resistance or short to ground
- Corroded or loose connectors in the fuel pump circuit
- Failing fuel pump control module (FPCM)
- Fuel pump with internal wear causing abnormal current draw
- Blown or incorrect amperage fuel pump fuse
- Internal ECM/PCM failure (less common)
2. Symptoms You Will Notice
- Engine cranks but does not start
- Loss of power or hesitation during acceleration
- Engine stalling shortly after starting
- Check Engine Light illuminated
3. Step-by-Step Diagnosis
Step 1: Check fuel pump fuse and relay; replace if blown or faulty.
Step 2: Use a multimeter to test voltage at the fuel pump connector; should be near battery voltage with key on.
Step 3: Inspect wiring and connectors for corrosion, damage, or loose connections.
Step 4: If voltage is low, back-probe the relay output; if voltage is good at relay but low at pump, repair wiring.
Step 5: If all wiring and relay are good, replace the fuel pump.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The vehicle may stall or fail to start, leading to a breakdown or accident.
How much does it cost to fix?▼
Repair costs range from $150 to $400, depending on whether it's a relay ($20-$50), wiring repair ($50-$150), or fuel pump replacement ($200-$400).
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.