P2797

Auxiliary Transmission Fluid Pump Performance

P2797 is a generic OBD-II powertrain diagnostic trouble code: Auxiliary Transmission Fluid Pump Performance. 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
P2797
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P2797 means

P2797 is stored when the TCM detects that the auxiliary transmission fluid pump is not delivering adequate flow or pressure for the current operating demand. Some modern automatic transmissions, particularly those used in hybrid vehicles or stop-start applications, are equipped with an electrically driven auxiliary pump that maintains hydraulic pressure when the engine-driven main pump is not spinning, such as during idle-stop events or during early hybrid launch phases.

When the control module commands the auxiliary pump and the resulting pressure or flow measured by the system falls below the calibrated minimum, P2797 is set. The transmission may disable idle-stop functionality, refuse to engage certain drive modes, or enter a protective shift strategy until the fault is resolved.

Possible causes include a failing auxiliary pump motor, blocked inlet strainer, low fluid level preventing adequate pump priming, wiring faults on the pump control or feedback circuits, or a faulty pump control module. Because the auxiliary pump is critical for smooth re-engagement after engine stop events, prompt diagnosis is advisable.

Common causes

Most-frequently reported root causes when P2797 is logged.

  • 1
    Worn or failing auxiliary transmission fluid pump motor.
  • 2
    Blocked or restricted auxiliary pump inlet strainer.
  • 3
    Low transmission fluid level preventing proper pump priming.
  • 4
    Open or short circuit in the auxiliary pump power supply or control wiring.
  • 5
    Faulty auxiliary pump control module or relay.
  • 6
    Air in the hydraulic circuit reducing pump output.
  • 7
    Internal pump wear causing insufficient output pressure.

Symptoms drivers notice

MIL or hybrid system warning light illuminated.
Idle-stop function disabled or unavailable.
Harsh engagement or jerk when the engine restarts after an idle-stop event.
Transmission entering a protective or restricted shift strategy.
Possible whine or noise from the auxiliary pump area during operation.

How to diagnose P2797

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and retrieve all DTCs; check for accompanying pump motor circuit or idle-stop system codes.
  2. 2
    Check transmission fluid level and condition, topping up as needed before further testing.
  3. 3
    Monitor auxiliary pump pressure or speed feedback PID with the scan tool during a commanded pump-on event.
  4. 4
    Inspect the wiring harness and connector for the auxiliary pump for damage or corrosion.
  5. 5
    Command the auxiliary pump on via bidirectional controls and listen for normal pump operation.
  6. 6
    Check the pump power supply fuse and relay if the pump does not activate on command.
  7. 7
    Inspect the auxiliary pump inlet strainer for blockage before replacing the pump assembly.

Vehicles where we've handled P2797

Platforms in our catalogue with confirmed P2797 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Which vehicles are most likely to set P2797?

Hybrid and mild-hybrid vehicles with idle-stop transmissions, and some conventional automatics designed for stop-start systems, are the most common applications.

Can low transmission fluid cause P2797?

Yes. If the fluid level is too low, the auxiliary pump may cavitate and fail to build adequate pressure, triggering the performance fault.

Will idle-stop work with P2797 active?

Typically no. The TCM disables idle-stop functionality when the auxiliary pump performance is compromised to prevent harsh re-engagement.

Is the auxiliary pump expensive to replace?

Auxiliary pump assemblies vary widely in cost depending on the vehicle. Confirming the pump is the actual fault rather than a wiring or strainer issue before replacement is important.

Disabling P2797 in software

RaceTune can permanently disable P2797 — 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 P2797 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 EDC17C50 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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