P0B04 indicates that phase V of the auxiliary fluid pump motor carries too little current, usually because the phase is open somewhere between inverter and winding. GM tests it on the Volt (2016) and in the 2018 and 2019 hybrid tables like its U and W siblings: in Run, with normal PWM, more than 50 V on the inverter and a minimum squared current command, the V current is sampled while the rotor sits within 30 degrees of the V axis. Under 1 A for 0.4 s out of 0.6 s (0.08 s windows in 2019) sets a Type A fault. GM bulletin PI1433 for the 2014-15 Spark EV names P0B04 with Service Vehicle Soon and reduced propulsion and points to the pump connector not being latched. P0B01 and P0B07 are phases U and W, P0B05 the high side, P0B03 the general V code.
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
- Service Vehicle Soon light and MIL
- Reduced propulsion power or limited vehicle speed
Most likely causes
- Pump motor connector not fully seated or latched (Chevrolet Spark EV)
- Open circuit in the phase V lead or terminal
- Phase V switch in the pump inverter not conducting
- Open winding of phase V in the pump motor
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P0B04 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- B: Subsystem depends on the code range
- 04: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0B04?
Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
What causes code P0B04?
The most common causes are: pump motor connector not fully seated or latched (Chevrolet Spark EV); open circuit in the phase V lead or terminal; phase V switch in the pump inverter not conducting.
Related codes
- P0B01Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current Low
- P0B03Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current
- P0B05Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current High
- P0B07Electric/Auxiliary Transmission Fluid Pump Motor Phase W Current Low
- P0C20Electric/Auxiliary Transmission Fluid Pump Phase U-V-W Circuit/Open
- P0C27Electric/Auxiliary Transmission Fluid Pump A Motor Current Low
Sources
- gsi.ext.gm.com: 16OBDG01 Hybrid Diagnostics
- gsi.ext.gm.com: 19OBDG02 Hybrid Diagnostics
- static.nhtsa.gov: MC 10113757 9999
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.