P2CBBFan 3 Underspeed
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2CBB concerns vehicles with three electric radiator fans: the third one turns slower than modelled for its command. GM's 2025 diesel table 25OBDG04B describes the check for a LIN-controlled fan 3. The controller converts the request into an expected speed, allows for start-up and ramp delays and for supply voltage, and compares the reported speed with a lower limit; at a 925 rpm request the floor is 725 rpm, at 2800 rpm it is 2600 rpm. Sixteen failures in twenty one-second samples set a Type B code, two trips to the lamp. The test only runs above 875 rpm and is blocked while U067C or the out-of-range fan 3 codes are active. Not every GM triple-fan setup uses P2CBB: table 23OBDG07 logs fan 3 underspeed under its own code P14D7. Overspeed is P2CBC, fan 2 underspeed P2CB9.
- What you may notice
- Check engine light after two trips
- Engine runs warmer under high load or in heat
- Reduced A/C cooling at low speed
- Likely causes
- LikelyFan 3 slowed by debris, ice or a distorted shroud
- PossibleFan 3 motor bearings or integrated controller worn
- PossibleVoltage drop on the fan 3 power feed or ground
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.