P0231 -- Fuel Pump Secondary Circuit Low Voltage

P0231 - Fuel Pump Secondary Circuit Low Voltage

Definition

• P0231 = Fuel Pump Secondary Circuit Low Voltage. Translation: Circuito secundário da bomba de combustível - Baixa voltagem. This code indicates the PCM/FPDM detected abnormally low voltage on the fuel pump's secondary circuit.

Context

• OBD-II uses standardized diagnostic trouble codes to indicate monitored faults in the powertrain and emissions-related systems. DTCs come from the vehicle's onboard monitors (powertrain codes are a subset focused on engine, fuel, and related systems).

• Emissions and fuel-management monitors are designed to protect engine performance and emissions; when the monitors detect out-of-range conditions, a code is stored and, in most cases, the Malfunction Indicator Lamp (MIL) is illuminated.

Purpose of this guide

• This guide provides a structured diagnostic approach for P0231 (fuel pump secondary circuit low voltage), with symptom-based descriptions, likely causes, and step-by-step testing procedures. It synthesizes the Open Source code definition and the general OBD-II diagnostic framework from .

Symptoms and user-reported complaints (typical, field experience)

• Engine cranks but does not start or runs briefly and stalls.
• Engine may start intermittently and then die, or run poorly with loss of power under load.
• Intermittent no-start conditions, especially after turning the ignition on or after hot soaking.
• MIL may illuminate in some cases; in others, the MIL may be off if the monitor hasn't yet retriggered.
  Note: These symptom patterns reflect common user-reported experiences for fuel-pump-related codes, including P0231, and align with the general purpose of fuel-pump related DTCs described in the OBD-II framework.

Probable Causes

• Faulty or corroded fuel pump relay or wiring in the secondary circuit (high frequency). This often results in intermittent or reduced voltage reaching the pump. Estimated likelihood: high.
• Wiring harness damage, poor or corroded connectors, or a bad ground in the secondary circuit (voltage drop to the pump). Estimated likelihood: high.
• Battery or alternator issues causing insufficient system voltage (overall electrical supply integrity affects secondary circuit voltage). Estimated likelihood: moderate.
• Faulty fuel pump primary/secondary circuit control module (FPDM/PCM) commanding or regulating voltage improperly. Estimated likelihood: moderate.
• Blown fuse or a pinched fuse/relay circuit in the fuel-puel pump circuit. Estimated likelihood: low to moderate.
• Actual fuel pump internal fault (though many pumps fail with mechanical wear, some failures present as undervoltage in the secondary circuit when the pump draws abnormally high current). Estimated likelihood: low to moderate.
  Notes on probabilities: These percentages are generalized estimates from field practice (ASE-like experience) and can vary by vehicle make/model and year. No specific NHTSA complaints data is cited here.

What to test and inspect (tools and prep)

• Tools
  • Scan tool capable of reading P-codes and live data
  • Multimeter or DVOM for voltage/current tests
  • Fuel pressure gauge (appropriate to vehicle; refer to service manual)
  • Fuel pressure tester with correct adapters
  • Basic hand tools (screwdrivers, pliers) and safety gear
  • Battery load tester or known-good battery for voltage testing
• Safety considerations
  • Relieve fuel pressure before disconnecting any fuel lines
  • Work in a well-ventilated area away from ignition sources
  • Disconnect the battery during hard wiring work; reconnect and recheck after repairs
  • Avoid creating sparks around fuel system components

Diagnostic procedure (step-by-step)

1) Confirm the code and gather data

• Use the scan tool to confirm P0231 is present and note any related codes (P0230, P0232, etc., if present).
• Check freeze frame data and recorded fuel rail pressure if available.
• Note battery voltage at key-on and during cranking if data is available; record any related data (engine temps, etc.).

2) Initial electrical health checks

• Battery and charging: ensure battery voltage is healthy (e.g., 12.6+ V with engine off; higher under cranking). A poor voltage supply can trigger low-voltage indications in the fuel-pump circuit.
• Fuses and relays: locate the fuel pump fuse and the fuel pump relay. Inspect for signs of corrosion or damage; test/swap the relay with a known-good unit if you can.
• Ground integrity: inspect grounds related to the fuel pump circuit and FPDM/PCM ground.

3) Check the fuel pump power supply at the pump connector

• With the ignition ON (and the engine allowed to crank if applicable to the vehicle), measure voltage at the fuel pump connector:
  • If pump supply is near battery voltage (roughly 12-13 V), the secondary circuit is being supplied correctly; the issue may be internal to the pump or FPDM-related.
  • If voltage is significantly lower (e.g., below ~9-10 V or showing high voltage drop under load), trace the supply wiring back toward the fuse/relay and through grounds. Look for resistance, corrosion, or loose connections.
• If the pump does not energize or voltage is inconsistent, suspect wiring, connectors, or control module as primary causes.

4) Pump operation and current draw check

• If safe and feasible, energize the pump (via jump or direct supply) to see if the pump spins reliably outside the vehicle. Note current draw:
  • Normal current draw varies by pump and vehicle; compare to manufacturer spec.
  • A pump that spins with no load but does not sustain operation in the car may indicate electrical supply issues (voltage drop) rather than a pump failure alone.
• If pump runs when directly powered, the problem likely lies in the control circuit wiring/faultyFPDM/PCM command rather than the pump itself.

5) Inspect harness, connectors, and routing

• Inspect the wiring harness to the fuel pump for chafing, pin damage, or water intrusion (especially if the vehicle has a known history of wiring issues in this area).
• Disconnect/connect the pump connector (with ignition off) to reseat and improve contact; check for bent pins or corrosion.

6) Fuel pressure test and pump performance

• Connect a fuel pressure gauge and compare measured pressure to the vehicle's spec when the pump is commanded ON (engine cranking or key-on, depending on vehicle design).
• If fuel pressure is low or fluctuates when commanded, this supports a pump, regulator, or supply issue in the circuit (consistent with P0231's low-secondary-circuit condition).
• If the pump voltage is correct but pressure is not, inspect for restriction, injector fault, or regulator issues that could indirectly affect voltage readings or PCM diagnostics.

7) FPDM/PCM and control logic considerations

• If the pump voltage and wiring check out, and the fuel pressure is within spec when the pump is energized directly, the FPDM/PCM may be misreading or failing to command proper voltage in the secondary circuit.
• In some vehicles, the PCM controls the pump's secondary circuit; a fault in FPDM/PCM can trigger P0231 even when the pump and wiring seem sound.
• This step may require specialist diagnostic tools or dealer-level support to further narrow down.

8) If no straightforward fix is found

• Re-check all wiring for intermittents after road testing or vibration tests.
• Consider replacing the fuel pump relay or FPDM if available and testable.
• Consider pump replacement if there is evidence of pump internal faults (even if voltage appears adequate in the controller-to-pump circuit, the pump itself may be failing internally).
• Re-test after each repair and clear the code; re-scan to confirm no reoccurrence.

Test data to collect and interpretation

• Battery voltage on key-on and during cranking; voltage drop across the pump circuit (both supply and ground).
• Actual pump voltage at the connector (under load) versus expected voltage.
• Fuel pressure with pump commanded ON; compare to spec.
• Relay continuity and coil resistance; wiring resistance from battery to pump and pump to ground.
• Any additional codes (P0230, P0232, etc.) that may illuminate broader fuel-system concerns.

Repair Options

• Repair or replace faulty wiring or connectors in the fuel pump circuit, especially where voltage drop is observed.
• Replace a faulty fuel pump relay or FPDM/PCM if diagnosed as the source of insufficient voltage in the secondary circuit.
• Repair or replace blown fuses or damaged fuse links in the fuel pump circuit.
• Address battery/alternator issues; restore proper voltage stability to the system.
• Replace the fuel pump if it has internal faults or severe wear that causes it to draw abnormal current or fail to maintain voltage delivery.
• After repairs, clear P0231, perform a drive cycle, and re-check for reoccurrence with a data-logging approach to confirm the issue is resolved.

Post-Repair Verification

• Confirm P0231 is cleared with a scan tool; perform a road test to verify the issue does not reoccur under normal operating conditions.
• Re-measure fuel pressure and pump voltage during a representative engine load condition to ensure consistent voltage delivery.
• Confirm there are no related codes (P0230-P0232) that could indicate broader fuel-pump circuit issues.

Notes on variability and sources

• The core definition linking P0231 to is drawn from the Open Source MIT repository (N/A, but the code name aligns with the description). This is the primary source for the code's meaning.
• The broader context of OBD-II, DTCs, and Powertrain Codes is anchored to on OBD-II and diagnostic trouble codes.
• This guide uses user-symptom patterns and common field-trial logic to inform symptom discussions and a practical diagnostic sequence. It does not introduce code meanings or procedures beyond what indicate, except where standard automotive diagnostic practice is broadly applicable (e.g., safety steps, general electrical checks, fuel-pressure testing).
• If conflicting information arises between sources, this guide mentions both perspectives and prioritizes the Open Source code definition for P0231 in its core meaning, while recognizing the general OBD-II diagnostic framework described by Wikipedia.

References (for further reading)

• Open Source (MIT) code definition: P0231 - Circuito secundário da bomba de combustível - Baixa voltagem (Secondary fuel pump circuit low voltage). This provides the direct code meaning.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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