Powertrain, generic (extended)

P2DE9 Cold Start Engine Coolant Pump Underspeed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Engines with an electric main water pump run it at a tightly metered speed after a cold start so the block heats quickly. P2DE9 flags that during this phase the pump turns too slowly. GM's 2025 ECM tables (25OBDG03B) filter the gap between requested and reported pump speed and fail the check when it exceeds 200 rpm for 8 of 10 seconds, with low-flow coolant mode and catalyst warm-up active, the request steady within 50 rpm for at least 3 s, and inlet coolant at −40 °C or warmer; two calibrated limits exist because the reachable speed depends on system voltage. Type B, MIL after two trips. Outside the warm-up phase the same fault is P2B85; pump faster than requested during cold start is P2E82. CARB demands such separate cold-start codes and a monitoring plan for electric water pumps.

Likely causes

Worn pump bearing or debris at the impeller slowing the rotor
Low supply voltage at the pump (battery, ground, connector)
Faulty pump electronics or speed feedback
Wrong or aged coolant, very thick when cold

Symptoms

  • Check engine light on after two trips
  • Uneven warm-up, local hot spots possible
  • Often no noticeable symptom

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–1,200
Time0.5–3 h

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

Parts involved

engine coolant pump

Related codes

P2B85P2E82P26CEP2C37P2DE8

References: gsi.ext.gm.com, law.cornell.edu.