Diagnostic article Generic OBD-II
P06CB: An incorrect-glow-plug code can be a live resistance-rationality result
Learn how the GM P06CB monitor derives resistance from voltage and current, and why it cannot prove that the wrong part was installed.
Read before applying this article
Documented application
2025 GM 04A documented monitor only. Vehicle, engine and controller calibration applicability must be established separately; no model fitment is inferred from the file.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P06CB is generically described as an incorrect cylinder 7 glow plug. The GM monitor is a resistance-rationality assessment: it calculates resistance from measured voltage and current and compares the result with a calibrated operating range. A stored code does not, by itself, prove that someone fitted the wrong part.
The measurements must be valid under command
The glow plug must be commanded on for the specified enable period, the glow system must be enabled and the relevant electrical and voltage-feedback fault conditions must be absent. The engine is running with cranking excluded, and supply must be in range.
These conditions matter because a resistance estimate depends on both measurements and an appropriate operating state. An off-state reading cannot substitute for the documented energized calculation, and a known feedback fault undermines the evidence used by the rationality check.
Keep the source's channel discrepancy visible
The heading identifies cylinder 7, but the malfunction sentence refers to glow plug 4. The document does not resolve that naming difference, so this article does not assign a physical plug or silently change the number. The intended channel must be established from the matching service information.
The table confirms fifteen failures within twenty-five samples at a 100-millisecond task rate, with two-trip reporting. Those monitor details support interpreting a repeated rationality result, while the source alone cannot distinguish a plug characteristic from a measurement-path problem or establish a replacement decision.
Source and applicability
2025 GM 04A 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 1004.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Cylinder 7 Glow Plug Incorrect
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT