Powertrain, generic (extended)

P2B87 Coolant Pump A Underspeed

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

With P2B87 the reported speed of coolant pump A stays below the commanded one. GM's 2025 tables (25OBDG03A, 25OBDG04B) compare filtered command and feedback against a calibrated limit while 300–3,480 rpm is requested and more than 11 V is present; 8 s in a 10 s window, Type B. Ford's 2024 gasoline summary lists it as the underspeed type of the cabin-heating auxiliary pump, checked continuously from 11 V. On GM vehicles the code often had no hardware cause: PIT5789 (2021 Tahoe, Suburban, Yukon, Escalade) cured it with new BCM software, bulletin 21-NA-024 (2021–2022 Acadia, Blazer, Enclave, Traverse, XT5, XT6) with an HVAC module update – the G17 pump was not to be replaced. PIT6505 later found a stray O-ring in it. Overspeed is P2B86, stall P2B9C.

Likely causes

Outdated software in the module that commands the pump
Impeller slowed by debris or a foreign O-ring
Worn bearing or motor in the auxiliary pump
Low voltage or poor contact at the pump connector

Symptoms

  • Check engine light, often without any other complaint
  • Reduced cabin heat at idle or with the engine stopped

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–600
Time0.3–3 h

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

Parts involved

coolant pump ahvac control modulebody control module

Related codes

P2B86P2B9CP2B9FP2BA0P2601

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