Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P1640: Control Module Output Circuit: Description
The ECM contains an Output Driver Module (ODM) which controls four circuits: A/C relay, main relay, EVAP vent solenoid and EVAP purge solenoid. The ODM controls each of these circuits independently by controlling the circuit ground. The ODM monitors the voltage level at each of the four circuits into the ECM when the device is being commanded on or off. When the device is commanded off (circuit not grounded), the voltage level at the ECM should be high (ignition voltage). When the device is commanded on (circuit grounded), the voltage level at the ECM should be low. Each of the four drivers in the ODM contains a feedback circuit used to determine if a particular circuit failed, which can be read on the Scan tool. DTC P1640 sets when any one of the four feedback voltages is low when that device is turned off or when any one of the four feedback voltages is high when that device is turned on when the engine is running.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.