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.
Circuit/System Testing: Notes
Each device may need to be disconnected to isolate a circuit fault.
Use the schematic to identify the following:
- Powertrain high speed CAN devices the vehicle is equipped with
- Powertrain high speed CAN serial data circuit terminating resistors
- Device locations on the powertrain high speed CAN serial data circuits
- Each device's ground, B+, ignition and powertrain high speed CAN serial data circuit terminals
Some devices with an internal terminating resistor have a loop in the harness that connects the internal terminating resistor to the serial data circuit. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground or open/high resistance prior to replacing the device for each of the following tests.
- Ignition OFF, all access doors closed, all vehicle systems OFF and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors with the powertrain high speed CAN serial data circuits at an easily accessible device that is not communicating. It may take up to 2 minutes for all vehicle systems to power down. Refer to Data Link References to determine which devices are on the powertrain expansion bus.
- Ignition ON.
- Test for less than 4.5 V between each powertrain high speed CAN serial data circuit at the device that was just disconnected and ground.
- If 4.5 V or greater
Refer to Testing the Serial Data Circuits for a Short to Voltage .
- If less than 4.5 V
- If 4.5 V or greater
- Ignition OFF, all access doors closed, all vehicle systems OFF and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
- Test for greater than 100 Ω between each powertrain high speed CAN serial data circuit at the device that was just disconnected and ground.
- If 100 Ω or less
Refer to Testing the Serial Data Circuits for a Short to Ground .
- If greater than 100 Ω
- If 100 Ω or less
- Test for 110-130 Ω between each pair of the powertrain high speed CAN serial data circuits at the device that was just disconnected:
- If less than 110 Ω
Refer to Testing the Serial Data Circuits for a Short between the Circuits .
- If greater than 130 Ω
Refer to Testing the Serial Data Circuits for an Open/High Resistance .
- If between 110-130 Ω
- If less than 110 Ω
- Refer to Testing the Device Circuits .
Use the Manual With the Right Hardware
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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.
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