P2B84 code meaning
Charge Air Cooler Coolant Pump A Underspeed
Powertrain system Generic code P2Bxx codes Check engine light
What P2B84 means
P2B84 reports that the electric charge air cooler pump is turning too slowly or not at all, judged by the speed its own electronics send back. GM lists the code next to P2B83 in the 2025 diesel table 25OBDG04B as the low out-of-range case of the pump speed, with the limit printed as a reading below -115 rpm; 8 failed one-second samples out of 10 are needed, with the pump fitted and enabled, relay voltage at 11 V or more and the engine not cranking. Type B, so the MIL comes on after the second faulty trip. Typical reasons are a seized bearing, debris at the impeller, a weak supply or a corroded connector – GM's bulletin 23-NA-102 found water entering the M10 pump plug on the 3.0-litre Duramax. With little flow the intake air runs hot.
P2B84 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor1 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2B84
- Check engine light after the second faulty drive
- Less power under heavy load or when towing
- High charge air temperature shown in live data
Common causes of P2B84
- Most likelyWorn or seized pump bearing, or debris blocking the impeller
- PossibleWater or corrosion in the pump connector
- PossibleLow supply voltage or poor ground at the pump
- Less likelyPump motor or its electronics worn out
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Cac coolant pump aCac coolant loop
What each part of P2B84 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| B | Area: hybrid propulsion. |
| 84 | The exact fault in that area. |
What to do next
- Note P2B84 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 P2B84
What does P2B84 mean?
P2B84 means "Charge Air Cooler Coolant Pump A Underspeed". P2B84 reports that the electric charge air cooler pump is turning too slowly or not at all, judged by the speed its own electronics send back. It is a generic code, so it means the same on every make.
Is it safe to drive with P2B84?
Drive gently and only to a workshop. With P2B84 the car can go into limp mode (reduced power) to protect itself.
Will P2B84 fail an emissions test?
Yes, it can. P2B84 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 P2B84 to fix?
Difficulty: medium. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will P2B84 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.