DME 7.2

P1674
497 Engine Compartment Purge Fan Output Stage - Open Circuit

P1674
497 Engine Compartment Purge Fan Output Stage - Below Limit

P1674
497 Engine Compartment Purge Fan Output Stage - Above Limit

Function
An engine compartment purge fan is installed to reduce the engine compartment temperature. The engine compartment purge fan is triggered by the DME control module as a function of the engine temperature, engine compartment temperature and vehicle speed.
Short circuit to ground and open circuit are detected when the output stage is blocked, short to B+ when the output stage is conducting.

Diagnosis conditions
- Engine running
- Battery voltage greater than 7 V
- Engine compartment purge fan switched on once


NOTE: The triggering wire for relay terminal 85 is monitored.

Wiring Diagram:

Diagnosis Procedure - Open Circuit:

Diagnosis Procedure - Short Circuit To Ground:

Diagnosis Procedure - Short Circuit To B+:

1 Check relay.

1. Remove relay.
2. Connect ohmmeter to terminals 85 and 86.
Display: approx. 75 ohms

2 Check wiring from DME control module to relay for continuity.

1. Connect special tool 9637 to wiring harness (DME control module connector).
2. Remove relay.
3. Connect ohmmeter to special tool 9637, pin II/20, and relay slot, pin 2 (terminal 85).
Display: 0 - 5 ohms

If infinity ohms is displayed, check wiring harness for chafing and pinching damage.

3 Perform adaptation.

1. Switch on the ignition.
2. Wait one minute. Do not press the accelerator.
3. Switch off the ignition for at least 10 seconds.
4. Read out the fault memory.


4 Check wiring from DME control module to relay for short circuit to ground.

1. Connect special tool 9637 to wiring harness (DME control module connector).
2. Remove relay.
3. Connect ohmmeter to special tool 9637, pin II/20, and ground.
Display: infinity ohms

If 0 - 5 ohms is displayed, check wiring for chafing and pinching damage.

5 Check wiring from DME control module to relay for short circuit to B+.

1. Connect special tool 9637 to wiring harness (DME control module connector).
2. Remove relay.
3. Connect voltmeter to special tool 9637, pin II/20, and ground.
Ignition on.
Display: 0 V

If battery voltage is displayed, check wiring harness for chafing and pinching damage.