Powertrain, generic (extended)

P24C4 EGR Cooler Bypass Position Sensor Exceeded Learning Limit Bank 1

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The bypass flap of the EGR cooler learns its end stops, and P24C4 means the learned values for bank 1 have left the window the software accepts. GM's diesel tables from 2017 on run the learning after key-off with coolant between 70 and 129 °C: the raw signal must lie between 16 and 24 % of 5 V in cooling position and between 72 and 85 % in bypass position; outside, the code is stored as Type B. GM's 2014 table 14OBDG10 instead judges the spread of the learned offsets (over 50 %) and a single offset beyond about ±16 %. Bulletin PI1449 for the 2015 Silverado and Sierra with the LML Duramax pairs it with P2493, P2495 and P06A3 and calls for a complete new bypass valve. Pure circuit faults are P2494/P2495; bank 2 reports P24C5.

Likely causes

Worn bypass valve whose integrated position sensor no longer reaches its learned values
Soot deposits shifting the end stops of the flap
Signal offset from connector corrosion or a weak 5 V reference
Learning repeatedly cut short because the controller is woken right after key-off

Symptoms

  • Malfunction indicator lamp on after the second trip
  • Reduced EGR cooling, higher NOx output
  • Often no change in driveability

Repair estimate

DifficultyHardWorkshop job
Parts and labour€250–1,200
Time1–4 h

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

Parts involved

egr cooler bypass position sensor b1

Related codes

P24C5P2493P2494P2495P245B

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