Fuel Trim Cylinder Balance Bank 1 (GM)
What does P1172 mean?
The P1172 code means the vehicle's onboard diagnostic system has detected: Fuel Trim Cylinder Balance Bank 1 (GM). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Rough idle
- Engine misfires on Bank 1
- Poor fuel economy
- Vibration at idle
Probable Causes (Ranked by Likelihood)
- Clogged or leaking fuel injector on Bank 1 Very High
- Intake manifold gasket leak on Bank 1 High
- Compression issue on one Bank 1 cylinder Moderate
- Ignition system fault (bad coil pack or spark plug) Moderate
- PCM fuel injector driver issue Low
Step-by-Step Diagnostic Procedure
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Perform a cylinder power balance test to identify the weak cylinder
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Test fuel injector resistance and flow on Bank 1 injectors
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Check compression on all Bank 1 cylinders
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Inspect spark plugs and ignition coils on Bank 1
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Check for vacuum leaks specific to Bank 1 intake runners
Frequently Asked Questions
What does fuel trim cylinder balance mean?
The PCM monitors individual cylinder contribution and fuel trim corrections. P1172 indicates one or more cylinders on Bank 1 require significantly different fuel trim than others, suggesting a cylinder-specific issue like a bad injector or compression loss.
How do I identify which cylinder is the problem?
Use a scan tool to perform a cylinder balance test, or check individual cylinder misfire counts in the misfire data. The cylinder with the highest correction or most misfires is likely the problem.
Can bad spark plugs cause P1172?
Yes. A fouled or worn spark plug on one cylinder can cause incomplete combustion, which affects that cylinder's fuel trim. Always check spark plugs before moving to more expensive diagnostics.