P2637

Fuel Pump B Control Circuit

P2637 is a generic OBD-II powertrain diagnostic trouble code: Fuel Pump B Control Circuit. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P2637
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2637 means

P2637 is a generic OBD-II code indicating the PCM has detected an electrical fault in the control circuit for fuel pump B. Unlike the performance-based P2636, this code specifically identifies a problem with the signal or command circuit that the PCM uses to control pump B operation, rather than a flow or pressure shortfall.

The control circuit typically involves a driver circuit within the PCM or a dedicated fuel pump control module that regulates pump speed via pulse-width modulation or a simple relay. A fault can be caused by an open or short in the command wire, a failed relay or control module, or a wiring harness defect. Some manufacturers use a separate fuel pump driver module (FPDM) between the PCM and the pump, and a fault in that module will also trigger this code.

When the control circuit fails the PCM may be unable to command the pump at all, resulting in a no-start or stalling condition, or it may run the pump at a fixed default duty cycle with reduced performance. Diagnosis should focus on the command circuit wiring and relay before moving to the pump itself.

Common causes

Most-frequently reported root causes when P2637 is logged.

  • 1
    Open circuit in the PCM-to-pump-B command wire.
  • 2
    Short to ground or to voltage on the control circuit wire.
  • 3
    Failed fuel pump relay for pump B circuit.
  • 4
    Faulty fuel pump driver module (FPDM) if equipped.
  • 5
    Corroded or loose PCM connector pin on the pump B output.
  • 6
    Blown fuse in the pump B control circuit.
  • 7
    Wiring harness chafe causing an intermittent short in the control path.

Symptoms drivers notice

MIL illuminated.
Engine may not start or stalls shortly after starting.
Intermittent loss of power under load if the pump defaults to a low duty cycle.
Fuel pressure may be absent or lower than specified.
Possible fuel pump relay chattering audible from the fuse box.

How to diagnose P2637

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and freeze-frame data with a scan tool to identify accompanying codes.
  2. 2
    Locate and inspect the fuel pump B fuse and relay; replace if faulty.
  3. 3
    Check for battery voltage at the pump B relay output and verify relay coil control from the PCM.
  4. 4
    Inspect the PCM-to-pump control wiring for opens, shorts, or damaged insulation.
  5. 5
    If a fuel pump driver module is present, check its supply voltage, ground, and communication signal.
  6. 6
    Perform a command test via scan tool if available to observe PCM output.
  7. 7
    Replace the relay, FPDM, or repair wiring as indicated by test results.

Related powertrain codes

Frequently asked questions

What is the difference between P2636 and P2637?

P2636 is a performance/flow fault where the pump runs but delivers insufficient pressure; P2637 is an electrical circuit fault where the PCM cannot properly command pump B.

Can a bad ground cause P2637?

Yes. A high-resistance or open ground in the pump B control circuit can prevent the PCM driver from completing the circuit, triggering a control-circuit fault.

Is the fuel pump driver module the same as the ECM?

No. Some vehicles use a separate FPDM to translate PCM commands into pump voltage; it is a distinct module and is a common failure point for this code.

Will clearing P2637 let me drive to a shop?

If the pump defaults to running at a fixed rate you may be able to drive short distances, but if the control circuit is fully open the engine may not start at all.

Disabling P2637 in software

RaceTune can permanently disable P2637 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECUs with a P2637 disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch MD1CS001 verified 1 software version

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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