P2B08 is the cold-start version of the cylinder 1 pulse check. While the catalyst is being heated, many direct-injection engines split each injection into two or three small pulses, and CARB requires for 20/50/100 % of model years 2026/2027/2028 that missing split or multiple pulses be detected during the cold-start strategy. CARB also wants faults found in that phase stored under their own codes, which is why P2B08 exists beside P2B00. GM used it earlier: its tables flag cylinder 1 when the opening signature is missing during catalyst warm-up, Type B. For the 1.2 L LIH in the 2020 Encore GX and 2021 Trailblazer, GM bulletin PIP5746 calls it a software anomaly appearing only on cold starts; verify after an overnight soak.
Medium severity. Can I keep driving?If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
Cylinder 1 is numbered according to the manufacturer: check your engine's manual before working on it.
Symptoms
- Warning lamp, often with the engine running normally once warm
- Possibly slightly rough running in the first seconds after a cold start
- Code returns only after a long standstill, not on warm restarts
Most likely causes
- Cold-start software anomaly (GM 1.2 L LIH, fixed by ECM reprogramming)
- Cylinder 1 injector sluggish when cold, missing the short split pulses
- Contact fault in injector 1 wiring that shows mainly when cold
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 P2B08 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- B: Subsystem depends on the code range
- 08: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2B08?
If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
What causes code P2B08?
The most common causes are: cold-start software anomaly (GM 1.2 L LIH, fixed by ECM reprogramming); cylinder 1 injector sluggish when cold, missing the short split pulses; contact fault in injector 1 wiring that shows mainly when cold.
Related codes
- P2B00Cylinder 1 Injection Pulse Performance
- P2B09Cold Start Cylinder 2 Injection Pulse Performance
- P2B95Cold Start Injection Pulse Performance
- P050DCold Start Rough Idle
- P0201Cylinder 1 Injector A Circuit/Open
- P0301Cylinder 1 Misfire Detected
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.