K6JRF at the mic K6JRF's Page
formerly W6FZC

My Mercedes Benz
S500 Coupe

K6JRF's MB S500 Cpe
(Updated: Mar 25, 2001)

Analyze and Troubleshoot "Check Engine" MIL and Electronic Control Units (ECU)!

Diagnostic Module N59

F23 Module Box with W140 ECUs
Diagnostic Module: Description and Operation
The Diagnostic module (N59) monitors the engine operation control systems and their ECU's to assist the technician during the troubleshooting/checking process. If the module detects a system/component malfunction, it illuminates the "CHECK ENGINE" light in the instrument cluster.

The Diagnostic module is located in the F23 module box and color coded PURPLE. The module is equipped with a memory that retains malfunctions codes even after the battery has been disconnected.

Check Engine Light in Istrument Panel
When the ignition module is switch ON, engine control system data is transmitted, via the CAN to the Diagnostic module and stored in memory. The Diagnostic module receives the necessary information from the following ECU's:
- LH-SFI control module (N3/1)
- EZL/AKR control module (N1/3)
- Electronic accelerator module (N4/1)
- ABS/ASR control module (N30/1)

If a system malfunction occurs, the diagnostic module receives a malfunction code signal from the appropriate ECU. If the same malfunction code occurs during TWO (2) consecutive trips, the CHECK ENGINE light is illuminated and remains lit until the malfunction is illuminated and the DTC reset.
The DTCs can be accessed via the diagnostic connector, X11/4 or the push button with LED, X11/21s1.

Fault Table, DTC Readout, Diagnostic Module (N59)

Socket 1: Black (Ground)
Socket 3: Red (+12.5V)
Socket 19: Yellow (Pin for DM DTC readout)

DTC Readout Possible Cause Remedy
1 No Faults in System -
2 Heated oxygen sensor inoperative Test LH-SFI unit
3 Lambda control inoperative Test LH-SFI unit
4 Air injection inoperative Test LH-SFI unit
5 Exhaust gas recirculation inoperative Test LH-SFI unit
6 Idle speed control inoperative Test electronic accelerator
7 Ignition system defective Test distributor igntion system
8 Engine coolant temperature sensor, open/short Test LH-SFI unit
9 Intake air temperature sensor, open/short Test LH-SFI unit
10 Voltage at mass air flow sensor too high/low Test LH-SFI unit
11 TN-signal (rpm) at LH-SFI control module (N3/1) defective Test LH-SFI unit
12 Heated oxygen sensor heater, open/short circuit Test LH-SFI unit
13 Camshaft position sensor signal of ignition control module (N1/3) defective Test LH-SFI unit
14 Intake manifold pressure at start in N1/3 too low/high Test LH-SFI unit
15 Wide open throttle information defective Test LH-SFI unit
16 Closed throttle position information defective Test electronic accelerator
17 Data exchange malfunction between individual control modules Test DM Step: 7.0
18 Adjustable camshaft timing solenoid, open/short circuit Test LH-SFI unit
19 Fuel injectors open/short or self-adaptation in LH-SFI control module (N3/1) at limit Test LH-SFI unit and reset adaptation to mean value
20 Speed signal not present Test electronic accelerator
21 Purge switchover valve, open/short circuit Test LH-SFI unit
22 Camshaft position sensor signal defective Test distributor system
23 Intake manifold pressure in N1/3 with engine running too high/low Vacuum supply to N1/3; Test distributor ignition system
24 Start ring gear segments and/or crankshaft position sensor defective Test distributor system
25 Knock sensors or ignition control module defective Test distributor system
26 Upshift delay 1 to 2 (model 123.034) , 2 to 3 (all models) Test LH-SFI unit
27 Engine coolant temperature sensor deviation between sensor ckt 1 and sensor ckt 2 Test LH-SFI unit
28 Engine coolant temperature sensor (coolant temperature change monitor Test LH-SFI unit

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