P278F

Transmission Friction Element B Apply Time Range/Performance

P278F is a generic OBD-II powertrain diagnostic trouble code: Transmission Friction Element B Apply Time Range/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
P278F
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P278F means

P278F mirrors P278B but applies to friction element B within the automatic transmission. The TCM monitors the hydraulic apply time for each clutch pack or band individually; when element B takes longer to engage than the calibrated threshold, P278F is stored. The specific gear event affected depends on which gear ratios element B controls in the particular transmission design.

Slow apply of friction element B typically manifests as a hesitation or RPM flare during the shift that relies on element B for gear establishment. Heat generated during prolonged slip damages the friction surfaces and accelerates wear of the steel separator plates.

Because this is a performance code rather than a circuit code, electrical diagnosis is not the primary path. Hydraulic pressure testing, fluid quality inspection, and solenoid performance evaluation are the appropriate starting points. If hydraulic pressure is adequate, internal mechanical wear of element B is the most likely finding.

Common causes

Most-frequently reported root causes when P278F is logged.

  • 1
    Worn friction element B clutch pack or band.
  • 2
    Faulty pressure control solenoid responsible for the element B circuit.
  • 3
    Low transmission fluid level reducing system pressure.
  • 4
    Degraded or oxidised transmission fluid losing viscosity.
  • 5
    Worn valve body bores causing pressure bleed-off.
  • 6
    Restricted transmission oil filter limiting pump output.
  • 7
    Leaking piston seal inside the element B hydraulic apply circuit.

Symptoms drivers notice

MIL illuminated.
Delayed or soft shift associated with friction element B engagement.
Engine RPM surge during the affected gear change.
Transmission slipping in the gear range dependent on element B.
Elevated transmission fluid temperature after repeated affected shifts.

How to diagnose P278F

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and freeze frame data to identify the specific shift event where the fault occurs.
  2. 2
    Verify transmission fluid level and inspect fluid condition for signs of burning or contamination.
  3. 3
    Perform a hydraulic pressure test on the circuit associated with friction element B.
  4. 4
    Use a scan tool to monitor the element B pressure control solenoid duty cycle and compare to specification.
  5. 5
    Replace the transmission fluid and filter as a baseline service if due.
  6. 6
    If pressure is within spec and solenoid performance is confirmed, evaluate for internal clutch pack wear.
  7. 7
    Proceed with transmission overhaul if internal wear is confirmed by pressure test or stall speed evaluation.

Related powertrain codes

Frequently asked questions

How do I know which shift uses friction element B?

Refer to the transmission-specific clutch and band application chart in the service manual; it maps each element to the gear ranges it supports.

Can P278B and P278F appear together?

Yes. Multiple friction element performance codes can be set simultaneously if there is a system-wide hydraulic pressure problem such as a worn pump or very low fluid level.

Is a transmission flush beneficial for this code?

A fluid and filter service is a reasonable first step, but a flush will not restore worn friction material or repair a leaking piston seal.

How serious is P278F compared to a slip code like P0732?

Both indicate slip, but P278F specifically captures a slow apply event. P0732 indicates the gear ratio is incorrect, which can be caused by sustained slip. They may occur together.

Disabling P278F in software

RaceTune can permanently disable P278F — 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.

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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