P249A is logged when the bank 2 bypass position signal sits near the top of the reference voltage. Like its siblings on this bank, it is not described by any manufacturer in public documents. The bank 1 analogue P2495 is set by GM's Duramax logic once the raw value exceeds 99 % of 5 V in most of a 250-sample window, rated Type B with the lamp after two trips. A reading stuck at the top usually means the sensor has lost its ground, so the signal floats up to the supply, or that the signal wire has contact with a voltage source. A water-damaged connector can produce the same picture. Because sensor and bypass valve are often one part, a new valve is only justified after wiring and ground check out. Low on bank 2 is P2499.
Medium severity. Can I keep driving?You can normally drive in moderation, but get it repaired soon: if the valve is stuck open, the engine may idle very poorly.
Bank 2 is the side without cylinder 1, so it only exists on V or boxer engines.
Symptoms
- Check engine light after two trips
- Bank 2 bypass position shows full scale
Most likely causes
- Lost ground at the bank 2 position sensor
- Signal wire in contact with a supply line
- Water ingress in the sensor connector
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P249A means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 4: Emissions
- 9A: Specific fault in that system
Frequently asked questions
Can I keep driving with code P249A?
You can normally drive in moderation, but get it repaired soon: if the valve is stuck open, the engine may idle very poorly.
What causes code P249A?
The most common causes are: lost ground at the bank 2 position sensor; signal wire in contact with a supply line; water ingress in the sensor connector.
Related codes
- P2495EGR Cooler Bypass Position Sensor Circuit High (Bank 1)
- P2497EGR Cooler Bypass Position Sensor Circuit (Bank 2)
- P2498EGR Cooler Bypass Position Sensor Range/Performance (Bank 2)
- P2499EGR Cooler Bypass Position Sensor Circuit Low (Bank 2)
Sources
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.