P0B08: Electric/Auxiliary Transmission Fluid Pump Motor Phase W Current High

P0B08 is set when the current in phase W of the auxiliary transmission fluid pump motor rises above the permitted limit. No manufacturer documents this exact code in public sources. In GM's 2016 Volt calibration the equivalent protection is P0C28, which fails on any phase above 35 A or on a d-axis current below a temperature-dependent limit, both within milliseconds to protect the IGBTs. A W-specific high code points to a short in the W lead or winding, a binding pump or a sensing error; the Hitachi patent shows the W value may be calculated rather than measured directly. CARB requires such output drivers to be monitored for circuit faults. The pump shuts down, so start-stop and electric driving are restricted. P0B07 is the low side, P0B02 and P0B05 phases U and V.

Medium severity. Can I keep driving?Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.

Symptoms

MIL and transmission or hybrid warning
Auxiliary pump shuts down, auto-stop disabled

Most likely causes

Phase W lead shorted to another phase or to ground
Pump binding mechanically, raising motor current
Current sensing in the pump inverter reads too high
Shorted turns in phase W of the pump motor

What to check, in order

Start with the simplest. You can tick off each step.

Check the fluid level and condition
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Read the input and output speed in live data
Check the connector and wiring
Check for other related engine codes
Consult the manufacturer's procedure for the transmission

Good to know

Repair difficulty: hard
It can trigger limp mode.
It affects emissions.

What each character of P0B08 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
B: Subsystem depends on the code range
08: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0B08?

Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.

What causes code P0B08?

The most common causes are: phase W lead shorted to another phase or to ground; pump binding mechanically, raising motor current; current sensing in the pump inverter reads too high.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.