P0B04 code meaning
Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current Low
Powertrain system Generic code P0Bxx codes Check engine light
What P0B04 means
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.
P0B04 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0B04
- Service Vehicle Soon light and MIL
- Reduced propulsion power or limited vehicle speed
Common causes of P0B04
- Most likelyPump motor connector not fully seated or latched (Chevrolet Spark EV)
- PossibleOpen circuit in the phase V lead or terminal
- PossiblePhase V switch in the pump inverter not conducting
- Less likelyOpen winding of phase V in the pump motor
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Aux trans pump motor phase vAux trans pump control moduleWiring harness
What each part of P0B04 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B | Area: hybrid propulsion. |
| 04 | The exact fault in that area. |
What to do next
- Note P0B04 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0B04
What does P0B04 mean?
P0B04 means "Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current Low". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0B04?
Drive gently and only to a workshop. With P0B04 the car can go into limp mode (reduced power) to protect itself.
Will P0B04 fail an emissions test?
Yes, it can. P0B04 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0B04 to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will P0B04 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.