HGV NOx Sensor Test Box User Guide
NOX SENSOR TESTING INSTRUCTIONS
With this tester you can identify common wiring faults to the NOx Sensor.
I will list a few common causes that you should be able to easily identify and then carry out a repair to the wiring based on your findings.
This tool is to aid you in your diagnosis, it will not let you the NOx sensors faulty. Unfortunately, we still have to a little bit of work to identify our fault. Which can be……
1.Short circuits: When wires to the NOx sensor touch each other in the harness (short to power) or with a rub through to touch the chassis (short to ground), it can cause a short circuit. This can lead to electrical malfunctions, blown fuses, or even electrical fires.
Image of a short to ground on the VOLTS supply. The NOx sensor tool is plugged in BUT no voltages are displayed which is usually identified by checking the fuse in the fuse box for a blown fuse.
Short to power faults can be identified on CAN-H and CAN-L by checking for voltage exceeding 2.8 volts.
2. Open Circuit: This is an example of an open circuit on CAN-H and CAN-L. An open circuit will not blow a fuse, but it will prevent the circuit from functioning. An open circuit may occur if a wire breaks, a wiring connector is loose or unplugged, or severe corrosion inside an electrical connector has created so much resistance that current cannot flow through the circuit.
3. High Resistance: Corrosion is a common cause of high resistance in electrical circuits. Which can be identified by green oxidised pins and terminals.
Corrosion can be caused by moisture that attacks electrical connectors and terminals in the electrical system. This is often displayed with low voltage readings on the VOLTS display. The vehicle should be outputting nearly 28 volts when running and around 24 volts with the ignition on. The measurement on VOLTS can be checked against your battery voltage to confirm the voltage is correct. If a large difference is noted, you could possibly have a resistance issue in your wiring harness which will need further investigation.
The same applies to your CAN-H and CAN-L, if you’re seeing voltages that are lower than 2 volts for CAN-H and CAN-L these wires will require further investigation and checking for resistance with the ignition off.
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