P2CB9Fan 2 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
- P2CB9 means the second electric cooling fan reports a lower speed than its command calls for, while communication and wiring are judged sound. GM uses it in two ways. In tables 23OBDG07 and 24OBDG07 the fan must stay below a speed-dependent floor of up to 3550 rpm for 20 s once it has been commanded above 7.65 % for more than 5 s. The 2025 diesel table 25OBDG04B models the expected speed of a LIN fan and flags 16 bad samples out of 20 at one per second, for example under 2300 rpm when 2500 rpm is asked for; both are two-trip codes with the lamp. GM's PIE0601 of 2020 lists P2CB9 with P0494, U0632 and U0633 on 2020–2021 full-size trucks and SUVs and asks for a look at fuses and debris in the blades. Fan 1 has P0494, overspeed of fan 2 is P2CBA.
- What you may notice
- Check engine light after two trips
- Coolant temperature rises at idle or when towing
- Weaker air conditioning at standstill
- Likely causes
- LikelyFan blades slowed by debris, leaves, snow or ice
- PossibleFan 2 motor or its integrated electronics worn or faulty
- PossibleBlown fuse, weak supply or poor ground at the fan
- RareSporadic entry without fault found (GM investigated without a fix)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.