P24EF code meaning
Control Module Wake-up Circuit/Open
Powertrain system Generic code P24xx codes Check engine light
What P24EF means
Some control modules drive a discrete wake-up output that switches other units on before or alongside the network. P24EF reports an open circuit on that line. GM uses it in the HPC2 battery-side processor of its 2016 and 2019 hybrid tables: with the output commanded off, a control voltage between 2.82 and 7.04 V counts as open, because an intact line would be pulled clearly low. The test samples every 12.5 ms and fails when 480 of 560 samples are bad, about seven seconds; it is Type A, so the MIL comes on after one trip. A broken wire, a backed-out pin or a module with a failed output are the typical reasons. The driver may face a module that does not wake up. P24F0 and P24F1 are the low and high faults.
P24EF at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P24EF
- Malfunction indicator lamp on
- Connected module stays asleep, with related communication codes
Common causes of P24EF
- Most likelyBroken wake-up wire in the harness
- PossiblePin pushed back or corroded in a module connector
- Less likelyWake-up output of the control module defective
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Wake up circuitControl moduleWiring harness
What each part of P24EF 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). |
| EF | The exact fault in that area. |
What to do next
- Note P24EF 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 P24EF
What does P24EF mean?
P24EF means "Control Module Wake-up Circuit/Open". Some control modules drive a discrete wake-up output that switches other units on before or alongside the network. It is a generic code, so it means the same on every make.
Is it safe to drive with P24EF?
Drive gently and only to a workshop. With P24EF the car can go into limp mode (reduced power) to protect itself.
Will P24EF fail an emissions test?
Yes, it can. P24EF 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 P24EF to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will P24EF clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.