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DTC codes / P02xx · Fuel and air metering (injector circuits) / P0231

P0231Fuel Pump Secondary Circuit Low

P0231 means the powertrain control module (PCM) has detected a low-voltage condition on the fuel pump secondary circuit, which is the monitoring or control side of the fuel pump relay and pump motor. The PCM expects to see voltage within a specific range on this circuit when the pump is commanded on, and a reading below that threshold sets this code.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering (injector circuits)

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Engine cranks but fails to start because the fuel pump does not prime or run
  • Engine stalls shortly after starting or during driving when the pump loses power
  • Intermittent no-start condition that may come and go with temperature or vibration
  • Rough running or loss of power under load if fuel pressure drops intermittently
  • Audible fuel pump prime may be absent when the key is turned to the run position

Common causes, most likely first

  1. Faulty fuel pump relay with burned or pitted contacts on the secondary circuit
  2. Damaged or corroded wiring in the fuel pump secondary circuit, including chafed insulation or broken strands
  3. Poor electrical connection at the fuel pump relay socket, inline connector, or fuel pump module harness
  4. Failed fuel pump motor drawing excessive current or having an open internal winding
  5. Blown fuse or fusible link that protects the secondary circuit, though this often sets additional codes
  6. Corrosion or water intrusion at the fuel pump module connector or relay box
  7. PCM driver circuit fault on the secondary control side, though this is less common

How to diagnose and fix it

  1. Inspect the fuel pump relay and swap it with an identical known-good relay to see if the code clears or the symptom changes
  2. Check all fuses and fusible links related to the fuel pump circuit with a test light or multimeter
  3. Perform a voltage drop test on the secondary circuit wiring from the relay to the fuel pump while the circuit is loaded
  4. Disconnect the fuel pump module connector and inspect terminals for corrosion, looseness, or water intrusion
  5. Measure fuel pump motor resistance and current draw against manufacturer specifications to rule out a failing pump
  6. Back-probe the PCM connector to verify the secondary circuit control signal is present and within range when the pump is commanded on
  7. Repair or replace any damaged wiring, connectors, or the fuel pump module as indicated by the test results, then clear the code and verify

What the secondary circuit really monitors

  • The secondary circuit is often the ground-side control or feedback path, not the main power feed, so a perfectly good fuel pump can still set P0231 if the relay ground or feedback wire is compromised.
  • A fuel pump relay that clicks does not guarantee good contacts; pitted relay contacts can pass enough current to prime the pump but drop voltage under load, setting a low-voltage code without a hard no-start.
  • Corrosion inside the fuel pump module connector is a frequent hidden cause, especially on vehicles driven in wet or salty conditions, and it can mimic a failed pump.
  • P0231 can be set by a PCM that misinterprets a normal voltage drop during pump prime, so always verify the circuit with a meter before condemning the pump or PCM.
  • Aftermarket alarms or remote start systems tapped into the fuel pump circuit can introduce resistance or intermittent shorts that trigger this code.

Can I keep driving with P0231?

If the engine starts and runs normally, you can drive cautiously to a repair shop, but avoid hard acceleration and long trips because the pump could fail completely without warning. If the engine cranks but will not start or stalls repeatedly, do not drive; have the vehicle towed to prevent a dangerous stall in traffic.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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