P277A

Code

Generic P — Powertrain

Electric/Auxiliary Transmission Fluid Pump B Hydraulic Leakage

Brand: Generic

Type: P — Powertrain

Views: UK: 47 EN: 43 RU: 31

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Page language: EN

Causes

Internal hydraulic leak inside Pump B (worn/failed vanes, seals, or housing)
External fluid leak in pump housing, lines, or fittings
Blocked or restricted return/charge passages in transmission or cooler
Low transmission fluid level or heavily contaminated fluid
Faulty pump motor (electrical failure) or excessive wear
Damaged wiring, poor connector connection, or short to ground/open circuit to pump

Symptoms

Transmission slip, delayed or harsh shifting
Low or fluctuating transmission line/charge pressure
Transmission control/limp mode or MIL illumination
Audible pump noise (whine/rattle) or no pump noise when commanded
Visible fluid leak under vehicle near transmission or auxiliary pump
Elevated transmission temperature or degraded performance

What to check

Scan for DTCs and view freeze-frame/livedata for pump command, pressure, and related codes
Visual inspection for external fluid leaks at pump, lines, fittings, cooler and transmission case
Check transmission fluid level and condition (contamination, metal particles)
Inspect wiring harness and connector for damage, corrosion, loose pins, or water intrusion
Measure pump supply voltage at connector while pump is commanded ON
Measure pump motor current draw (compare to factory spec) to detect internal mechanical drag or short

Signal parameters

Command duty cycle or request status: 0–100% (varies by vehicle)
Battery voltage at pump connector: ~11–14.5 V when engine on
Pump motor current draw: typically small tens of mA to several A (manufacturer spec required)
Target hydraulic/line pressure when pump commanded: should rise above baseline (typical transmission line pressures ~50–200 psi; consult service data)
Pressure sensor voltage range: typically 0.5–4.5 V proportional to pressure (check OEM curve)
TCM fault counters/timeout intervals (stored in module data/freeze-frame)

Diagnostic algorithm

Retrieve all stored codes and freeze-frame data; note drive conditions when code set.
Visually inspect pump B, mounting, hoses, lines, fittings and transmission area for external leaks; repair any obvious leaks.
Check fluid level and condition; top or replace fluid if low or contaminated and re-test.
Inspect electrical connector and wiring for damage, corrosion or water ingress; secure and repair as needed.
With a scan tool, command Pump B on and observe pump command, duty cycle, pressure sensor, and related parameters in real time.
Measure voltage at pump power and ground while commanded; verify good supply and ground continuity back to fuse/TCM.
Measure pump motor current while commanded; compare to specification to detect mechanical failure or internal short.
Attach a calibrated hydraulic pressure gauge to the appropriate test port; command the pump and verify pressure rise and hold for expected value.
If pressure does not reach specification but electrical supply and current are normal, suspect internal hydraulic leakage or internal pump failure — consider pump removal and bench test or replacement.
If pressure and electrical checks OK but TCM reports leakage, verify pressure sensor operation (bench or substitute known-good sensor) and inspect internal transmission passages/valves for leakage.
Repair or replace faulty components (pump, lines, sensors, wiring, TCM software update) per OEM procedures. Clear codes and perform road test with re-scan to confirm repair.
If intermittent or unclear, consult OEM service information for special tests, pressure test procedures, and recommended replacement items.

Likely causes

Worn internal pump components causing inability to build/hold pressure
Damaged pump housing or loose/failed hydraulic line/fitting causing external leakage
Contaminated fluid or clogged filter/strainer restricting flow to/from pump
Connector corrosion or broken wiring causing reduced voltage/current to pump
Faulty pressure sensor or incorrect sensor signal interpreted as leakage

Fault status

⚠️ Status

P277A — Electric/Auxiliary Transmission Fluid Pump B hydraulic leakage detected. Pump commanded but hydraulic pressure/flow below expected threshold; TCM may limit operation and set MIL/limp mode.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 2-6 hours