Powertrain, generic (extended)

P2BA0 Coolant Pump C Underspeed

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2BA0 reports that coolant pump C does not reach its speed. GM names the code Low Temperature Coolant Loop Pump Underspeed in its diesel ECM tables and treats it as a low out-of-range speed reading: in 2020 (20OBDG04) the printed limit is below -100 rpm in 5 of 8 one-second samples, in 2025 (25OBDG04A) below -50 rpm in 4 of 5; enable conditions are an active pump, 11 V or more at the relay and no cranking. Type B, so the lamp waits for a second faulty trip. Bulletin 21-NA-149 lists P2BA0 among the many codes caused by a chafed engine harness on the 3.0-litre LM2 Duramax in 2021 trucks and SUVs, next to P2C48 for the same pump. Besides wiring, a stuck or worn pump and air in the loop are suspects. Pump B is P2B9F, pump D P2BA1.

Likely causes

Engine harness chafed against brackets, shorting pump circuits
Worn or partly seized low-temperature loop pump
Air or low coolant in the low-temperature loop
Low supply voltage at the pump relay

Symptoms

  • Check engine light after the second faulty trip
  • Parts on the low-temperature loop cooled less, reduced power possible
  • Further electrical codes when the harness is damaged

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–800
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

coolant pump cwiring harnessecm

Related codes

P2C48P26F4P26F8P26FAP2B9FP2BA1

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.