P0B0B

Code

Generic P — Powertrain

Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 26 EN: 51 RU: 27

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Page language: EN

Causes

Short to battery positive (B+) on pump A supply wiring
Failed pump motor internal electronics or diode(s)
Malfunctioning pump power relay or stuck contact
Faulty pump motor driver / power transistor in TCM or pump control module
Charging system overvoltage (faulty voltage regulator/alternator)
Poor or open ground causing a high reading on the measurement circuit

Symptoms

MIL/Warning lamp illuminated
Pump runs continuously or not at all depending on failure mode
Transmission shift irregularities or limp-home mode
Reduced transmission cooling or abnormal fluid temperature
Noise from pump or no pump noise when expected
Stored or intermittent fault symptoms depending on wiring/charging state

What to check

Use a scan tool: read freeze frame, live data and confirm P0B0B is current or stored
Inspect pump connector, wiring harness and ground for corrosion, damage or signs of heat
Check fuses and pump-related relays for proper operation
Measure vehicle battery/charging voltage at rest and while running
Backprobe pump supply connector: measure voltage with key ON engine OFF, engine running, and while pump is commanded ON
Disconnect pump electrical connector and re-check supply voltage at harness terminal

Signal parameters

Typical 12 V system battery/charging voltage: ~11–15 V (system dependent)
High-voltage threshold (example): >15.5 V may register as 'high' (verify manufacturer spec)
Pump supply when commanded ON: near battery voltage or PWM-modulated between 0–battery V
Pump supply when disabled: near 0 V or open-circuit at controller output
Motor coil resistance: typically low (fractions of an ohm up to a few ohms) — consult pump spec
Controller PWM frequency (varies by manufacturer): commonly ~100–2000 Hz

Diagnostic algorithm

Confirm code and gather data: read all stored and pending DTCs and capture freeze-frame and live data for pump supply voltage and system voltage.
Visual inspection: inspect wiring harness, shielded leads, connector pins and grounds for corrosion, damage, melting or poor connection at pump, TCM and battery/alternator.
Check vehicle charging system: measure battery voltage with engine off and running; ensure alternator regulator is not overcharging (compare to manufacturer spec).
Backprobe and measure: with key ON (engine OFF) measure voltage at pump supply pin and ground. Then command pump ON via scan tool and measure voltage. Document values.
Isolate load: disconnect pump connector and re-measure supply voltage at harness. If voltage remains high with pump disconnected, suspect wiring short to B+ or module fault. If voltage drops to expected, suspect pump internal fault or short inside pump.
Check grounds and continuity: measure resistance to chassis ground from pump ground and module ground. Repair any high-resistance or open grounds.
Inspect relays/fuses: test or substitute the pump power relay if applicable. Verify relay contacts are not welded or stuck.
Verify control signal: check TCM/pump driver output for expected PWM or switching behavior using an oscilloscope or diagnostic tool per factory procedures.
Component substitution/testing: if wiring and grounds check good, consider bench-testing or replacing the pump or substituting a known-good module/relay per workshop capability.
Repair, clear codes and re-test: repair identified faults, clear DTCs, perform a functional test and road test to confirm the fault does not return.

Likely causes

Wiring short to B+ at or near pump connector
Failed pump internal circuitry causing supply rail to be pulled high
Stuck/ welded relay contacts that keep battery feed applied incorrectly
Alternator/voltage regulator allowing system overvoltage
Open or high-resistance ground on pump circuit or module reference ground
Faulty TCM/pump driver reporting incorrect voltage

Fault status

⚠️ Status

P0B0B — Electric/Aux Transmission Fluid Pump A Motor Supply Voltage Circuit High: Detected supply voltage above allowable threshold on Pump A motor circuit. Inspect wiring, grounds, pump and charging system.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours