01 Navigating Truck Accidents: How an 18 Wheeler Truck Lawyer … • 02 5 Things You Should Know About Oxygen Sensors in Cars • 03 What Does CC Mean in Car Engines? A Complete Guide to Engin… • 04 The Benefits of ABS: Why You Need This Safety Feature in Yo… • 05 Ford’s Iconic Blue Oval Logo Gets a Refresh • 06 What Depth of Water Can I Drive Through With My Car? • 07 A Comparison of Planetary and Bevel Gears: Types, Functions… • 08 What Happens If You Press the Throttle and Brake Together i… • 09 A Complete Guide To Diesel Particulate Filter (DPF) • 10 Tips for Extending the Life of Your Automatic Transmission … •

DTC codes / P26xx · Computer and output circuits / P263B

P263BMIL Control Circuit High

P263B means the engine computer has detected an abnormally high voltage on the circuit that controls the Malfunction Indicator Lamp (MIL), the check engine light itself. The computer expects to be able to switch the lamp on and off by pulling that control wire low, and a high voltage reading tells it the circuit is open, shorted to power, or the driver inside the computer has failed.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • The check engine light may be stuck on continuously or may not illuminate at all when the key is first turned on.
  • Often no symptoms besides the warning light, because the fault is in the lamp control circuit rather than the engine management system.
  • Other warning lamps or dashboard illumination may behave erratically if the MIL shares a ground or power feed.
  • A failed state inspection or emissions test because the MIL self-test does not complete correctly.
  • In some vehicles the engine may run normally with no drivability complaint at all.

Common causes, most likely first

  1. Open circuit in the MIL control wire between the engine computer and the instrument cluster or lamp driver.
  2. Short to battery voltage on the MIL control circuit, often from chafed wiring near a sharp edge or a pinched harness.
  3. Failed instrument cluster or lamp driver module that no longer responds to the computer's control signal.
  4. Corroded or loose connector pins at the engine computer or cluster, creating high resistance that the computer reads as high voltage.
  5. Internal driver failure inside the engine computer, leaving the MIL control output stuck high.
  6. A blown fuse or poor ground shared by the instrument cluster, which can bias the control circuit voltage high.

How to diagnose and fix it

  1. Clear the code and verify it returns; note whether the MIL actually illuminates during the key-on bulb check.
  2. Inspect the engine computer and instrument cluster connectors for corrosion, backed-out pins, or water intrusion.
  3. Check the MIL control wire for continuity from the computer connector to the cluster connector, looking for opens and shorts to power.
  4. Measure voltage on the control circuit with the key on and the computer commanding the lamp off; a constant high reading confirms the fault.
  5. Test the instrument cluster or lamp driver with a known-good unit or a bidirectional scan tool that can command the MIL on and off.
  6. Repair or replace the damaged section of harness, the cluster, or the engine computer as indicated by the tests.
  7. After repair, clear codes and confirm the MIL performs a normal bulb check and the code does not reset.

When the check engine light itself is the fault

  • A P263B can set even when the engine runs perfectly, because the code monitors the lamp control circuit and not any engine sensor or actuator.
  • Technicians often replace the instrument cluster first, but a chafed control wire shorted to power will set the same code and is far cheaper to fix.
  • Some vehicles route the MIL control through a body control module or smart junction box, so the fault may live there rather than at the engine computer or cluster.
  • A weak or missing ground at the instrument cluster can pull the control circuit voltage high and mimic a failed computer driver.
  • If the MIL never lights during the key-on self-test, suspect an open control circuit before condemning the lamp bulb or cluster.

Can I keep driving with P263B?

The vehicle is safe to drive because this code affects only the check engine light control circuit and not engine operation, but you should repair it promptly so the MIL can warn you of future faults and so the vehicle passes emissions inspection.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage