P262B: Control Module Power Off Timer Performance

P262B concerns the timer that keeps counting inside a control module while the vehicle is shut down, used to measure how long it has been off. GM runs two checks on it: a count-up test while run/crank is inactive, failing when two consecutive readings differ by over 1.5 s in 4 of 20 one-second samples, and a range test comparing the hardware timer with a mirror timer at shutdown or restart (deviation above 25 % in the 2014 tables). It is Type B, so the MIL follows on the second trip. GM saw false sets on 2019–2020 CT6 4.2 L engines when the engine cooled faster than expected, for example in wind or an air-conditioned garage (PIP5754: clear the code and keep the ECM), and links P262B to ECM supply or ground faults (PIP5609) and to a lost ignition relay feed (PIT5391).

Symptoms

• MIL on after two drive cycles
• Possibly other control module codes stored at the same time

Most likely causes

• Poor ECM power or ground connection, momentary supply loss
• Ignition relay or its control circuit not supplying the module
• Diagnostic calibration too sensitive to fast engine cool-down
• Internal timer hardware fault in the control module

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the battery and grounds
2. Compare the reading with other engine data while varying the engine speed.
3. Clear the code and see if it returns
4. If it is a reference voltage code, disconnect sensors one at a time and see if the voltage recovers
5. Check whether a software update is available
6. Do not replace the control module without a full diagnosis

Good to know

• It affects emissions.

What each character of P262B means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 6: Control modules and outputs
• 2B: Specific fault in that system

Frequently asked questions

Can I keep driving with code P262B?

It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

What causes code P262B?

The most common causes are: poor ECM power or ground connection, momentary supply loss; ignition relay or its control circuit not supplying the module; diagnostic calibration too sensitive to fast engine cool-down.

Related codes

• P2610ECM/PCM Internal Engine Off Timer Performance
• P0606Control Module Processor
• P0601Internal Control Module Memory Checksum Error
• P062BInternal Control Module Fuel Injector Control Performance
• P0513Incorrect Immobilizer Key

Sources

• gsi.ext.gm.com: 14OBDG01 Hybrid Diagnostics
• static.nhtsa.gov: MC 10181167 9999
• static.nhtsa.gov: MC 10151817 9999
• static.nhtsa.gov: MC 10139374 9999

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.