Powertrain, generic (extended)

P27A5 Electric/Auxiliary Transmission Fluid Pump B Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P27A5 sets when the control line of auxiliary pump B sits at a level that only a connection to a voltage source can explain. In practice the wire touches a powered conductor, or moisture links it to a neighbouring supply pin. No manufacturer documents P27A5 publicly. For pump A, GM's 2025 TCM tables call the equivalent P2799 and judge it by an impedance below 0.5 Ω from signal to a voltage source in 20 of 25 checks, carried out only while the relevant driver is active and supply voltage is between 9 and 15 V; it is a Type B fault. Depending on how the circuit is built, such a short can leave pump B unable to switch off, which links this code to P27A6. Audi's pump B is the V553 on its 0CJ, 0CK and 0CL gearboxes. Repair centres on the harness; the pump itself is seldom at fault.

Likely causes

Control wire chafed against a powered conductor
Moisture bridging the control pin to a supply pin
Faulty output stage in the controlling module

Symptoms

  • Stop-start switched off
  • Pump B may run continuously or not at all
  • MIL after two trips on Type B systems

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

aux trans pump bwiring harness

Related codes

P27A2P27A4P27A6P2799

References: gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.