Scania COO DTC 844 CAN communication with switch module

COO Coordinator · Scania · 4 variants

Code 844 (decimal). Some diagnostic tools show it in hexadecimal as 034C.

In short

Fault in communication with the switch module in the steering wheel.

Variant 1

Applies to: COO10 (COO)

What does Scania COO fault code 844 mean?

Fault in communication with the switch module in the steering wheel.

What causes Scania DTC 844?

The cause may be one of the following: - The switch module is not connected to the switch module CAN network, or there is a break in the cable harness on the switch module sub data bus. - Fault in the wake-up signal or voltage supply. - Defective switch module.

How does the system react?

Yellow warning indication of a coordinator fault is displayed.

What are the symptoms?

Degradation of functions connected to the switch module.

How to fix Scania COO fault code 844?

  1. Check the connections and cable harness for an interruption (eroded, defective, unconnected pins) in the cable harness on the switch module sub data bus.
  2. Check the connections and cable harness for a short circuit (eroded, defective, unconnected pins) on the wake-up signal and switch module voltage supply.
  3. Check the resistance on the switch module sub data bus:
  4. Measure the resistance between CAN high and CAN low of the switch module in question with the battery disconnected.
  5. The resistance should be approx.
  6. 60 ohms.
  7. Measure the resistance between CAN high of the switch module in question and CAN high of the other units on the switch module sub data bus, with the battery disconnected.
  8. The resistance should be approx.
  9. 0 ohms.
  10. Measure the resistance between CAN low of the switch module in question and CAN low of the other units on the switch module sub data bus, with the battery disconnected.
  11. The resistance should be approx.
  12. 0 ohms.
  13. If the fault cannot be rectified, renew the switch module on the steering wheel.

Variant 2

Applies to: COO8 (COO)

Detection

Fault in communication with the switch module on the steering wheel.

Possible cause

The cause may be one of the following: - The switch module is not connected to the switch module CAN network, or there is a break in the cable harness on the switch module sub data bus. - Fault in the wake-up signal or voltage supply. - Defective switch module.

Symptoms

Degradation of functions connected to the switch module.

How to fix

  1. Check the connections and cable harness for an interruption (eroded, defective, unconnected pins) in the cable harness on the switch module sub data bus.
  2. Check the connections and cable harness for a short circuit (eroded, defective, unconnected pins) on the wake-up signal and switch module voltage supply.
  3. Check the resistance on the switch module sub data bus:
  4. Measure the resistance between CAN high and CAN low of the switch module in question with the battery disconnected.
  5. The resistance should be approx.
  6. 60 ohms.
  7. Measure the resistance between CAN high of the switch module in question and CAN high of the other units on the switch module sub data bus, with the battery disconnected.
  8. The resistance should be approx.
  9. 0 ohms.
  10. Measure the resistance between CAN low of the switch module in question and CAN low of the other units on the switch module sub data bus, with the battery disconnected.
  11. The resistance should be approx.
  12. 0 ohms.
  13. If the fault cannot be rectified, renew the switch module on the steering wheel.

Variant 3

Applies to: COO9 (COO)

Detection

Fault in communication with the switch module on the steering wheel.

Possible cause

The cause can be one of the following: - The switch module is not connected to the switch module CAN network or open circuit in the cable harness on the switch module sub data bus. - Fault in the wake-up signal or supply voltage. - Defective switch module.

Symptoms

Degradation of functions connected to the switch module.

How to fix

  1. Check the connections and cable harness for an open circuit (pins with verdigris, defective, not connected) in the cable harness on the switch module sub data bus.
  2. Check the connections and cable harness for a short circuit (pins with verdigris, defective, not connected) on the wake-up signal and switch module voltage supply.
  3. Check the resistance on the switch module sub data bus:
  4. Measure the resistance between CAN high and CAN low of the switch module concerned with the battery disconnected.
  5. Resistance should be around 60 ohms.
  6. Measure the resistance between CAN high of the switch module concerned and CAN high of the other units on the switch module sub data bus, with the battery disconnected.
  7. Resistance should be around 0 ohms
  8. Measure the resistance between CAN low of the switch module concerned and CAN low of the other units on the switch module sub data bus, with the battery disconnected.
  9. Resistance should be around 0 ohms.
  10. If the fault cannot be rectified, renew the switch module on the steering wheel.

Variant 4

Applies to: COO8

Detection

Fault in communication with the switch module on the steering wheel.

Possible cause

The cause can be one of the following: - The switch module is not connected to the switch module CAN network or open circuit in the cable harness on the switch module sub data bus. - Fault in the wake-up signal or supply voltage. - Defective switch module.

System reaction

- Degradation of functions connected to the switch module. - The warning is displayed in the instrument cluster (depending on configuration).

How to fix

  1. Check the connections and cable harness for an open circuit (pins with verdigris, defective, not connected) in the cable harness on the switch module sub data bus.
  2. Check the connections and cable harness for a short circuit (pins with verdigris, defective, not connected) on the wake-up signal and switch module voltage supply.
  3. Check the resistance on the switch module sub data bus:
  4. Measure the resistance between CAN high and CAN low of the switch module in question with the battery disconnected.
  5. Resistance should be around 60 ohms.
  6. Measure the resistance between CAN high of the switch module in question and CAN high of the other units on the switch module sub data bus, with the battery disconnected.
  7. Resistance should be around 0 ohm.
  8. Measure the resistance between CAN low of the switch module in question and CAN low of the other units on the switch module sub data bus, with the battery disconnected.
  9. Resistance should be around 0 ohm.
  10. If the fault cannot be rectified, renew the switch module on the steering wheel.

This information is for guidance only. Always follow the manufacturer workshop manual and safety procedures; if in doubt, contact an authorised workshop.

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