Diagnostic article Generic OBD-II
P0640: Intake-heater control response while heating is commanded off
P0640 evaluates the intake-air heater control response through the glow-plug controller in this GM diesel system.
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Documented application
2009 General Motors diagnostic parameter file 09OBDG01 DURAMAX Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established.
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.
P0640 is an intake-air heater switch/control-circuit check in GM's Duramax summary. The glow-plug control module evaluates a digital response associated with a heartbeat signal. The documented test occurs with the intake-air heater commanded off.
An off-state test can reveal a control fault
The source describes a high response while the heartbeat signal is active as the failure condition. This does not mean that the controller directly measured inadequate intake heating. The distinction matters because a warm intake reading or a heater that sometimes operates cannot establish that the monitored off-state response is correct.
The failure must persist for 650 milliseconds, and the test is conducted every two seconds. These timings belong to the documented electronic check; they are not instructions to energize the heater manually or bridge its high-current control circuit.
Preserve the command and response relationship
A useful diagnostic record identifies heater command status, the relevant controller faults and the response evidence available through the prescribed diagnostic equipment. The code alone does not establish which switch, wiring segment or controller element is defective.
Use the exact vehicle's heater and glow-plug-controller service procedure. High-current heater circuits require the specified testing method. Verification should demonstrate a correct control response and completed monitoring under the required off-command condition. Clearing P0640 or judging intake warmth alone leaves the actual electrical-response question unanswered.
Source and applicability
2009 General Motors diagnostic parameter file 09OBDG01 DURAMAX Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.
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
Intake Air Heater Control Circuit
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