P27A6

Code

Generic P — Powertrain

Electric/Auxiliary Transmission Fluid Pump B Stuck On

Brand: Generic

Type: P — Powertrain

Views: UK: 19 EN: 82 RU: 29

AI status

Completed

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Page language: EN

Causes

Stuck relay or relay contacts welded closed supplying battery voltage to pump
Short to battery voltage in pump wiring or connector (backfeed)
Failed pump control transistor/MOSFET inside TCM/PCM/module forcing output on
Internal pump failure (stuck internal valve) creating a condition that the controller compensates for
Corroded/shorted connector pins or damaged harness
Incorrect software or calibration issue in transmission control module

Symptoms

Pump audible noise when engine off or when pump should be idle
Parasitic battery drain / vehicle battery discharging
Reduced fuel economy and increased electrical load
Transmission with abnormal temperature readings or reduced shift quality
MIL (malfunction indicator lamp) or transmission warning light illuminated
Stored P27A6 diagnostic trouble code and possibly related codes

What to check

Read freeze frame and related DTCs from transmission and powertrain modules
Visual inspection of pump harness, connectors and relay for corrosion, damage or melted insulation
Check for voltage present at pump positive terminal with ignition off (indicates relay/short)
Identify and remove the pump relay; test if condition persists
Measure pump current draw and compare to specification
Inspect for software updates or technical service bulletins (TSBs) for pump control

Signal parameters

Supply voltage to pump: battery voltage ~12–14.5 V when energized
Control signal from TCM/PCM: low-side PWM or switched ground (0 V to near battery voltage at driver), duty cycle varies with demand
Typical PWM frequency: commonly 50–500 Hz (manufacturer-specific)
Expected off-state: control output near battery voltage (open/high‑side) or near 0 V (open low‑side) depending on circuit; pump should draw ~0 A when not commanded
Typical running pump current: varies by model; often several amps (measure to compare with spec)

Diagnostic algorithm

Retrieve and record freeze frame and all related codes. Check for stored events that show when pump was commanded.
With ignition OFF, inspect harness, connectors and relay for visible damage or water ingress. Remove any corrosion and secure connections.
Identify pump relay/fuse. With ignition OFF, remove the pump relay. If voltage is still present at the pump connector with the relay removed, suspect a short to battery in the harness or an additional feed.
With connector accessible, measure voltage at the pump feed and control pins with ignition OFF and then with key ON/engine running while commanding pump with a scan tool. Note any unexpected battery voltage present when pump should be off.
Measure current draw at the pump while commanded on and while off. High current or current when off indicates stuck motor or backfeed.
If the pump receives battery voltage only when the control module commands it on, monitor the control output with a lab scope or high-quality DVOM to see if the module output is stuck in the energized state. Compare PWM duty/frequency to expected values.
Isolate the pump: disconnect pump connector and operate the vehicle or command the pump. If the code clears and pump no longer runs, the fault is in pump or harness. If pump still receives power when disconnected, fault is upstream (relay/short/module).
Test or replace relay with known-good unit and retest. If fault persists and wiring checks clean, suspect module driver failure.
Check for relevant software updates or TSBs; update control module software if recommended.
Replace the faulty component only after verifying root cause: wiring repair, relay replacement, pump replacement, or control module repair/reprogram as required. Clear codes and perform road test to confirm repair.

Likely causes

Relay or external relay driver stuck closed (common)
Short to battery voltage in harness or connector feeding pump
Failed output stage inside the transmission control module
Contaminated or mechanically seized pump causing abnormal control behavior

Fault status

⚠️ Status

Transmission control module reports Electric/Auxiliary Transmission Fluid Pump B is stuck on (pump remains energized when not commanded). Diagnostic monitoring detected continuous pump operation or unexpected feed to pump circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours