P278B

Transmission Friction Element A Apply Time Range/Performance

P278B is a generic OBD-II powertrain diagnostic trouble code: Transmission Friction Element A 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
P278B
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P278B means

P278B is set when the TCM detects that friction element A (a clutch pack or band) is taking longer to apply, or applies more slowly, than the calibrated time window allows. The TCM monitors apply time by comparing commanded hydraulic pressure events against measured turbine or output shaft speed changes. If the gear ratio does not shift within the expected time, the code is stored.

Slow apply times are generally caused by insufficient hydraulic pressure reaching the friction element, worn friction material that requires more pressure to engage, or air intrusion into the hydraulic circuit. In some cases, a faulty pressure control solenoid supplying element A is the direct culprit.

This fault can produce noticeable shift quality complaints, including soft or delayed upshifts and a tendency for the transmission to hang in gear before completing a shift. Prolonged slip during apply increases heat and wear. Diagnosis should include a hydraulic pressure test for the circuit associated with friction element A and a fluid condition inspection.

Common causes

Most-frequently reported root causes when P278B is logged.

  • 1
    Worn friction element A clutch pack with insufficient clamping force.
  • 2
    Faulty or weak pressure control solenoid for the friction element A circuit.
  • 3
    Low transmission fluid level reducing available hydraulic pressure.
  • 4
    Degraded transmission fluid with reduced viscosity.
  • 5
    Valve body wear causing pressure bleed-off in the element A circuit.
  • 6
    Blocked transmission filter restricting fluid supply.
  • 7
    Internal transmission seal failure allowing pressure bypass around element A piston.

Symptoms drivers notice

MIL illuminated.
Soft, delayed, or prolonged upshift associated with friction element A.
Engine RPM flare during the affected shift.
Transmission slipping during acceleration in the affected gear range.
Possible burnt smell from transmission overheating due to extended slip.

How to diagnose P278B

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool, retrieve all DTCs, and note which gear range or shift event corresponds to element A.
  2. 2
    Check transmission fluid level and condition; replace if burnt or contaminated.
  3. 3
    Perform a line pressure test and compare measured pressure in the element A circuit to specification.
  4. 4
    Monitor pressure control solenoid command and feedback PIDs with the scan tool during the affected shift.
  5. 5
    Inspect and replace the transmission filter if restricted.
  6. 6
    If pressure is within spec and solenoid operation is confirmed, internal clutch pack wear is likely.
  7. 7
    Plan transmission overhaul or replacement if internal wear is confirmed.

Vehicles where we've handled P278B

Platforms in our catalogue with confirmed P278B coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

What is friction element A?

The designation A refers to a specific clutch pack or band within the transmission's gear-train. The exact element varies by transmission make and model.

Can a transmission fluid change fix P278B?

If the cause is degraded fluid or a slightly restricted filter, a fluid and filter service may resolve the fault. It will not repair worn friction material.

Is P278B the same as a slipping transmission?

P278B is a performance code indicating slow application time, which is a form of slip during gear engagement. It is more specific than a general slip complaint.

Can I drive the vehicle with P278B active?

Short-term driving is possible but will accelerate wear of the friction element. Repair as soon as practical to avoid more costly internal damage.

Disabling P278B in software

RaceTune can permanently disable P278B — 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 P278B 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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