Fuel Delivery
P0231
Fuel Pump Secondary Circuit Low
P0231 — Fuel Pump Secondary Circuit Low — applies to Fuel Pump Electrical Control and identifies circuit low input. The monitored item is fuel pump control circuit. The code wording tells you what the module judged; it does not prove the named…
Diagnostic Snapshot
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Learn the System
Before diagnosing this code, it helps to understand the system behind it.
Read Understanding Fuel Delivery SystemsTechnical Summary
P0231 — Fuel Pump Secondary Circuit Low — is a Hero-tier chapter covering fuel pump control circuit. The exact monitored fault is circuit low input.
The module evaluates the secondary pump output/feedback circuit for voltage below the calibrated expectation when the pump is commanded on. Freeze-frame matters because enabling logic may depend on voltage, temperature, elapsed time, load, command state, and absence of blocking DTCs.
Start with proof: Separate the primary command circuit from the secondary high-current pump/output circuit and test both under load. Then use the correct wiring diagram, graphing data, and an independent physical or waveform/current test to establish whether the result is electrically false or mechanically real.
Do not invent universal voltage, resistance, current, duty-cycle, pressure, or boost specifications. Sensor and driver architecture varies; manufacturer service data and safety procedures take priority.
Safety/driveability: A stall or no-start may occur if pump power is lost. If the engine cuts out unpredictably, towing is safer than continued driving. Risk if ignored: Low directly, but stalling is a safety concern and high-resistance pump wiring can overheat connectors.
What You'll Learn
- Exact meaning of P0231
- Monitor and enabling-condition logic
- Freeze-frame and live-data clues
- Electrical versus physical test direction
- Repair verification
Think Like a Technician
Treat P0231 as evidence, not a parts order. The module is evaluating the secondary pump output/feedback circuit for voltage below the calibrated expectation when the pump is commanded on.
First prove whether the electrical path is credible. Then decide whether the physical system follows the command. A good sensor or actuator should not be replaced simply because the system around it is abnormal.
What This Code Means
P0231 — Fuel Pump Secondary Circuit Low — applies to Fuel Pump Electrical Control and identifies circuit low input. The monitored item is fuel pump control circuit. The code wording tells you what the module judged; it does not prove the named part has failed.
The module evaluates the secondary pump output/feedback circuit for voltage below the calibrated expectation when the pump is commanded on. Exact enabling criteria and thresholds vary by calibration and may depend on voltage, temperature, load, run time, prerequisite sensor validity, and protection-state logic.
Start with proof: Separate the primary command circuit from the secondary high-current pump/output circuit and test both under load. Then test the exact circuit and compare scan data with the physical system so an electrical fault is not confused with a real throttle, pump, boost, or injector problem.
System Overview
Fuel Pump Electrical Control supplies feedback or controlled action used by the PCM to manage engine torque, fuel delivery, boost, and emissions. Diagnose the chain of command/input, circuit integrity, physical response, and feedback.
Why This Code Sets
The monitor for P0231 runs only when the module has enough valid information to judge fuel pump control circuit. Prerequisites vary by calibration.
Once enabled, the module evaluates the secondary pump output/feedback circuit for voltage below the calibrated expectation when the pump is commanded on. P0231 is stored when the result remains outside the calibrated expectation long enough or through the required samples.
The wording—circuit low input—determines test priority. High/low/circuit faults favor electrical testing; range/performance/overboost faults require proving whether the signal is electrically wrong or the physical system truly missed its target.
Common Symptoms
- Check Engine Light
- Possible emissions-test failure
- Hard start or no-start
- Intermittent stall
- Loss of power under load
Most Likely Causes
- 1. fuel-pump relay/control-module circuit fault
- 2. fuse/feed problem
- 3. poor pump/module ground
- 4. high-resistance tank/body connector
- 5. damaged wiring
- 6. fuel pump drawing abnormal current
- 7. fuel-pump control module fault
- 8. PCM command/feedback fault after external proof
Common Vehicles
Generic OBD-II code used across many makes; exact applications, component naming, driver strategy, cylinder numbering, boost hardware, and monitor thresholds vary. Verify the specific VIN.
Freeze Frame Clues
- System voltage
- RPM/load/vehicle speed
- ECT/IAT and time since start
- Key Fuel Pump Electrical Control command/feedback PIDs
- Throttle/fuel-trim/fuel-pressure context where relevant
- Companion codes sharing power/ground/control causes
- Cold-start vs hot-soak vs acceleration/high-load context
Live Data Expectations
Graph fuel-pump command/duty, pump-module status, fuel pressure where available, system voltage, RPM, and load. Commanded-on with low output voltage favors feed/ground/relay/module resistance; voltage present when commanded off favors a stuck relay or short. Pressure is a consequence check because the DTC describes the electrical path.
Typical Verification Tests
- Confirm P0231 absent from current/pending memory
- Recreate freeze-frame operating range
- Graph key command/feedback for plausible response
- Repeat wiggle/heat/load test if intermittent
- Perform required relearn/adaptation
- Verify no related code appears
- Complete applicable readiness monitor
- Confirm original complaint is resolved
Before You Condemn
- Confirm VIN-specific definition/component identity
- Save freeze-frame/pending/related codes
- Verify system voltage and grounds
- Inspect connector/terminal fit
- Compare scan command/feedback with independent physical or waveform/current test
- Run OEM circuit/functional test
- Rule out mechanical/flow/boost/fuel causes
- Document the failed test
Before Replacing Parts
Save freeze-frame and verify the exact component/circuit. Separate the primary command circuit from the secondary high-current pump/output circuit and test both under load. Replace parts only after a failed circuit, waveform/current, command-response, or OEM functional test is documented.
Diagnostic Workflow
- Confirm P0231 with a capable scan tool and save current, pending, and history DTC status. Do not clear memory before recording evidence.
- Save freeze-frame and companion codes. Record RPM, load, vehicle speed, ECT, IAT, system voltage, throttle position, fuel trims, and the system-specific command/feedback PIDs.
- Verify the VIN-specific code definition, component naming, connector pinout, circuit design, monitor prerequisites, and service precautions.
- Inspect fuel pump control circuit connector and harness for corrosion, terminal tension, chafing, heat damage, fluid intrusion, previous splices, and poor routing.
- Verify battery and charging-system voltage are stable before judging marginal sensor, relay, actuator, or injector-driver behavior.
- Separate the primary command circuit from the secondary high-current pump/output circuit and test both under load.
- Identify the primary relay/module command side, secondary/output side, and any fuel-pump control-module feedback circuits from the wiring diagram.
- Command the pump on with a scan tool when supported and measure voltage at the relay/module/pump under load.
- Perform voltage-drop testing across the pump power and ground paths; open-circuit voltage alone can hide resistance.
- Check relay control, relay contacts, fuses, module grounds, and any inertia/cutoff device used by the vehicle.
- Measure pump current with an approved method; excessive or unstable current can indicate a failing pump or overloaded circuit.
- On variable-speed systems, compare commanded duty/speed with actual output/feedback rather than applying full battery voltage indiscriminately.
- Inspect tank/body connectors for heat discoloration, spread terminals, moisture, and resistance heating.
- If the external circuit is correct but control/feedback remains wrong, test the pump control module/PCM using OEM procedure.
- Repair the proven relay, feed, ground, connector, module, wiring, or pump fault.
- Recreate the original start/load condition and verify stable pump operation with no current or pending P0231.
Labor & Inspection Checklist
- Verify VIN/engine and service information
- Scan all modules/save freeze-frame
- Inspect component/connector/harness
- Check relevant pump/boost/charge-air/throttle/injector basics
- Perform circuit test
- Compare live data with independent physical or waveform/current test
- Repair/relearn
- Complete monitor verification
Common Repairs
- Repair proven wiring/connector/power/ground/reference fault
- Replace fuel pump control circuit only after testing proves internal failure
- Correct verified throttle, pump, boost-control, charge-air, or injector cause
- Perform required relearn/adaptation
- Complete monitor verification and confirm no pending DTC
Common Parts
- Connector pigtail
- Harness repair materials
- Sensor/solenoid/relay/module only if proven
- System-specific mechanical parts only after diagnosis
Shop Notes
Monitor logic for P0231: the DTC is meaningful only after the module's enabling conditions are met. Check system voltage, temperature, load, related-sensor validity, and blocking DTCs before assuming the named circuit or component is the first failure.
Electrical proof for P0231: inspect terminal fit before relying on continuity. Use a high-impedance meter/scope for sensor circuits and an appropriate loaded test for relay, pump, solenoid, or injector circuits.
Physical proof for P0231: if the electrical path is credible, verify the system it controls. Check actual throttle movement, pump output, desired-versus-actual boost, wastegate/VGT motion, charge-air integrity, or injector current/contribution as appropriate.
Intermittent strategy for P0231: reproduce heat, vibration, engine movement, boost load, or harness movement while graphing the affected PID. Save the trace so the failure can be compared directly with post-repair data.
Related-code strategy for P0231: shared references, fuel-pressure codes, throttle-correlation codes, boost codes, misfire codes, or system-voltage faults can reveal a common cause.
Repair verification for P0231: repeat the original operating condition, confirm the previously abnormal signal or response is corrected, complete the monitor, and check pending memory.
Technician Notes
Diagnose the wording of P0231: circuit low input.\n\nThe monitor evaluates the secondary pump output/feedback circuit for voltage below the calibrated expectation when the pump is commanded on.\n\nEfficient first move: separate the primary command circuit from the secondary high-current pump/output circuit and test both under load.\n\nPreserve freeze-frame until the root cause is proven.
Mechanic's Tip
For P0231, graph the affected command and feedback on the same screen. The first signal to deviate usually shows whether the problem begins in the circuit, mechanical system, or feedback sensor.
Common Mistakes
- Replacing fuel pump control circuit from the code name alone
- Clearing freeze-frame too early
- Using universal voltage/resistance/current/boost values instead of OEM data
- Checking continuity without loaded testing or terminal-fit inspection
- Ignoring shared power/reference/ground circuits
- Ignoring companion boost/fuel-pressure/misfire/throttle codes
- Skipping relearn or monitor verification
Tools Used During Diagnosis
- Enhanced graphing scan tool
- Digital multimeter
- OEM wiring diagram/service information
- Backprobe/terminal test tools
- Battery/charging-system tester
- Current clamp
- Loaded-circuit voltage-drop equipment
- Fuel-pressure data/test equipment when needed
Manufacturer Notes
Generic OBD-II definition. Fuel-pump architecture ranges from a simple relay to variable-speed control modules. Primary/secondary terminology and feedback circuits vary; use the exact wiring diagram before interpreting voltage.
Customer Explanation
Your vehicle stored P0231, meaning the computer found circuit low input in the Fuel Pump Electrical Control system. The code does not automatically prove fuel pump control circuit is bad; wiring, control circuits, and real mechanical conditions can create the same result.
Frequently Asked Questions
What does P0231 mean?
P0231 means the module identified circuit low input involving fuel pump control circuit. It describes the failed monitor, not automatically a failed part.
Can I drive with P0231?
A stall or no-start may occur if pump power is lost. If the engine cuts out unpredictably, towing is safer than continued driving.
What should I check first for P0231?
Separate the primary command circuit from the secondary high-current pump/output circuit and test both under load. Save freeze-frame and related codes before clearing anything.
Does P0231 prove the named component is bad?
No. Wiring, connectors, shared power/reference/grounds, control modules, real mechanical conditions, and the component itself can create the same DTC.
Will P0231 affect an emissions inspection?
Usually yes if the MIL is commanded on, and clearing the code immediately before inspection can leave readiness monitors incomplete.
Can low system voltage contribute to P0231?
Yes. Weak cranking or charging voltage can distort sensor references, relay/module behavior, electronic-throttle control, and injector-driver diagnostics.
Should I clear P0231 before diagnosing it?
No. Freeze-frame, pending codes, companion codes, and readiness status can show exactly when the monitor failed.
When is professional equipment justified for P0231?
When visual inspection and basic circuit checks do not prove the cause. A graphing/bidirectional scan tool, oscilloscope/current clamp, smoke/pressure equipment, and OEM service information may be required.
Can P0231 be intermittent?
Yes. Heat, vibration, terminal fretting, harness movement, sticking boost actuators, relay contacts, and injector-driver faults can disappear in the shop.
How do I verify the repair?
Recreate the original operating condition, confirm the affected command/signal behaves normally, complete the applicable monitor, and verify the code is absent from current and pending memory.
Related Atlas Resources
Use the related Atlas system chapter plus VIN-specific OEM service information for specification-level testing.
Diagnostic Confidence
High after the fault is reproduced and the electrical/physical cause is proven; Medium when the event is intermittent and cannot be reproduced
Related Codes
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