P2187: Bank 1 lean-at-idle evidence comes from the additive trim component

P2187 is the bank 1 system-too-lean-at-idle entry. The cited GM gasoline monitor evaluates the additive portion of long-term fuel trim. It is not a universal threshold applied to any scan-tool field that happens to be labeled fuel trim.

Identify the correction component being compared

The published failure boundary is additive bank 1 trim above 5.48 percent. Additive mixture adaptation must be active, and the enable logic also requires stable multiplicative adaptation under suitable operating conditions. The continuation includes more than ten seconds of stability and limits on variation in correction and operating state.

The two trim components therefore serve different roles in this assessment. A transient short-term correction or an unidentified combined trim value cannot simply be substituted for the additive quantity named in the row.

Separate evaluation time from learning readiness

The threshold row lists a 0.2-second evaluation and two-trip reporting. That short interval does not remove the preceding adaptation and stability requirements. A quick idle observation immediately after a state change may not reproduce a valid test opportunity.

Retain the exact additive parameter, adaptation-active status and stable operating context for bank 1. The code does not identify an air leak, fuel-delivery defect or oxygen-sensor failure by itself, and the document supplies no universal replacement rule. Vehicle-specific parameter definitions and diagnostic information are needed before linking the learned correction to a physical cause.

Source and applicability

2025 GM 07A-1 documented monitor only. Vehicle, engine and controller calibration applicability must be established separately; no model fitment is inferred from the file. GM PDF, physical page 241; GM PDF, physical page 242.