Powertrain, generic (extended)

P24D4 EGR Cooler Coolant Pump Feedback Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Where an electric auxiliary pump moves coolant through the EGR cooler, the pump usually reports back to the engine controller on a separate wire, for example with a speed or status signal. P24D4 is the general fault of that feedback circuit: the signal is missing or cannot be interpreted, while the narrower cases of a line stuck below or above its band are P24AC and P24AD. The drive side may be fine; faults in the control line are P24A7 to P24AA. No manufacturer documents P24D4 publicly. CARB requires the controller to check inputs from emission-related components for circuit faults and rationality. Pierburg describes EGR coolers as part of the coolant circuit. Without valid feedback the controller cannot prove the cooler is supplied and may cut back EGR to protect it.

Likely causes

Open feedback wire or loose connector at the pump
Failed pump electronics no longer sending a status signal
Blown fuse or failed relay leaving the pump without power

Symptoms

  • Malfunction indicator lamp on
  • EGR reduced, possibly higher NOx and changed engine noise
  • Coolant temperature warnings if the pump really stops

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–700
Time0.5–3 h

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

Parts involved

egr cooler coolant pump

Related codes

P24ACP24ADP24A7P24A8

References: law.cornell.edu, ms-motorservice.com.