P27A5

Code

Generic P — Powertrain

Electric/Auxiliary Transmission Fluid Pump B Control Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 36 EN: 47 RU: 41

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Page language: EN

Causes

Short to battery voltage in pump B control wiring
Stuck or welded relay controlling pump B (relay contacts stuck closed)
Failed auxiliary transmission fluid pump B (internal short or seized)
Poor or corroded connector or wiring causing intermittent high voltage reading
Faulty ground or fused bypass creating elevated circuit voltage
Transmission control module (PCM/TCM) driver output damaged

Symptoms

Transmission warning lamp or MIL illuminated
Auxiliary transmission pump B runs continuously or does not run when commanded
Transmission overheating or abnormal transmission temperature rise
Harsh shifting, delayed gear engagement, or limp-home mode
Unusual noise from pump area or high electrical current draw (fuses may blow)

What to check

Read and record freeze frame and all transmission-related trouble codes
Visually inspect pump B connector, wiring harness, and nearby components for damage, corrosion, pin damage, or signs of heat
Check related fuses and relays (inspect relay for welded contacts)
Back-probe pump B control connector and monitor voltage while commanding pump ON/OFF with scanner
Measure resistance of pump motor with connector disconnected
Check ground integrity and continuity from pump ground to chassis/engine ground

Signal parameters

Battery supply voltage (key ON/engine running): ~12.0–14.5 V
Expected control driver OFF voltage:
Expected control driver ON voltage: near battery voltage (when internally switched high) or PWM varying between 0–14.5 V depending on design
Typical auxiliary pump motor resistance (disconnected): ~1–30 ohms (manufacturer dependent)
Typical running current: varies widely — commonly a few amps up to 20–30 A under load for transmission auxiliary pumps (check vehicle spec)
PWM duty cycle: 0–100% depending on commanded flow/pressure (if used)

Diagnostic algorithm

Verify the code with a scan tool and note freeze frame data and any related transmission or powertrain codes.
Inspect harness and connector at pump B for corrosion, melted insulation, pin damage, or water intrusion. Repair as needed.
Check fuses and the pump power/relay circuit. Remove and inspect the relay for welded contacts or test by substitution.
With connector disconnected, measure pump motor resistance to check for internal short or open. If resistance is abnormally low (near short) or open/infinite, replace pump.
Back-probe the pump B control pin. Command pump ON and OFF with a scanner while monitoring voltage and current. Confirm whether the module is commanding correctly and whether circuit voltage goes high when it should be low.
Check for a short to battery on the control circuit: with key off, measure continuity to battery positive. If present, isolate wiring sections to find short.
Verify ground continuity from pump ground to chassis; repair any poor ground connections.
If wiring, connectors, relay, and pump are good, suspect a damaged driver inside the PCM/TCM. Confirm with manufacturer diagnostic procedures before replacing the control module.
After repairs, clear codes and perform a test drive or functional test to confirm proper pump operation and that the code does not return.

Likely causes

Short to battery on the pump B control circuit
Stuck relay or control device powering the pump continuously
Failed pump motor with internal short or mechanical seizure
Corroded connector or damaged wiring at pump harness

Fault status

⚠️ Status

Control circuit voltage on Electric/Auxiliary Transmission Fluid Pump B is higher than expected. DTC stored; check wiring, relay, pump, and module driver.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours