P24C4 code meaning
EGR Cooler Bypass Position Sensor Exceeded Learning Limit Bank 1
Powertrain system Generic code P24xx codes Check engine light
What P24C4 means
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.
P24C4 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of P24C4
- Malfunction indicator lamp on after the second trip
- Reduced EGR cooling, higher NOx output
- Often no change in driveability
Common causes of P24C4
- Most likelyWorn bypass valve whose integrated position sensor no longer reaches its learned values
- PossibleSoot deposits shifting the end stops of the flap
- PossibleSignal offset from connector corrosion or a weak 5 V reference
- Less likelyLearning repeatedly cut short because the controller is woken right after key-off
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
EGR cooler bypass position sensor b1
What each part of P24C4 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| C4 | The exact fault in that area. |
What to do next
- Note P24C4 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P24C4
What does P24C4 mean?
P24C4 means "EGR Cooler Bypass Position Sensor Exceeded Learning Limit Bank 1". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P24C4?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P24C4 fail an emissions test?
Yes, it can. P24C4 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P24C4 to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will P24C4 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.