K6JRF at the mic K6JRF's Page
formerly W6FZC


My Mercedes Benz
S500 Coupe

K6JRF's MB S500 Cpe
(Updated: Jan 25, 2007)

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

Engine Management Systems
The Bosch LH/EZL Computerized Engine Control System electronically regulates the air/fuel mixture, idle speed, and ignition timing to achieve the optimum engine performance. Optimum performance means the best possible compromise between the demands for high power, low fuel consumption and the cleanest possible exhaust emissions.

Advanced electronic control units (ECU) evaluate the functions such as ignition and fuel injection, making minute and instantaneous adjustments to help maximize power and torque while minimizing emissions and avoiding knock. A computer-balanced crankshaft spins with virtually no trace of vibration. Also a double-row steel timing chain is employed for durability.

Engine Management Block Diagram

Engine Management Block Diagram

Take time to study this functional schematic showing the interrelations between all of the Engine Management Systems present in the vehicle. Understanding these 'blocks' give a comprehensive knowledge when attempting to repair one of the faulty systems.

The system uses three (3) interconnected Electronic Control Units (ECU); one controlling the fuel injection, one controlling the ignition system and finally one controlling the electronic accelerator system.

All three systems have self-diagnostics and fault code storage. All faults can be accessed through the 38 pin diagnostic socket, X11/4 or the push button with LED (X11/21s1).

The self-diagnostics is performed by the Diag Module (N59). The module constantly monitors engine performance by comparing its programming window with the values it receives via the Controller Area Network (CAN). When a programming parameter has been exceeded, a retrievable fault code is stored.

If the Diag Module detects a serious fault code in the engine control system, it activates the 'CHECK ENGINE' light. By extracting the fault codes via the X11/4 socket or PB/LED, the faulty component can be identified and then tested further.

Fuel Injection System
The LH fuel injection system is based on the Bosch multi-port fuel injections system with mass airflow sensor (LH-Jetronic). This ECU uses electrical inputs from various devices and sensors to calculate engine load and condition. With this information, it adjusts the injection duration and timing to provide optimum air/fuel mixture for performance, drivability and emissions compliance.

Adaptive Memory
Time and mileage affect the operation of both the injection and the idle control systems. To compensate for wear and deposit accumulation, the LH system modifies its basic programming to provide for efficient operation under all driving conditions. If the system determines that it must modify it basic programming beyond the preset window limit, a fault code is stored in the self-diagnostic memory.

Limp Home Operation
If the ECU determines that the mass air flow signal is incorrect or missing, the system enters a preset 'limp-home' mode. In this mode, preset injection duration is operational such that the car may be driven to an MB shop for repair.

Ignition System
The ignition system is based on the electrically controlled Bosch system with knock control. The ECU uses electrical input signals from various devices and sensors to calculate the engine temperature, load and speed. With this information, the ECU adjusts the ignition timing to provide optimum performance, economy and emissions.

Electronic Accelerator System
This ECU is equipped with an electronically controlled accelerator pedal/throttle plate. The Electronic Accelerator (N4/1) controls the idle speed. This system keeps the engine within a constant RPM when at idle. The system compensates for cold engine, high engine load or other influencing factors.

Testing the Engine System
To read and analyze the DTC, make sure the ignition key is set to the full 'ON' position. All warning lights should be on. To recall and reset CHECK ENGINE light codes on vehicles that use LH or HFM type fuel injection, the Diagnostics Module (DM) must be read. The faults must be cleared from the DM to shut off the CHECK ENGINE light on these vehicles.

On vehicles with HFM type fuel injection, after checking for HFM fault codes, also check the EA/IC/ISC control unit for fault codes. On vehicles with LH type fuel injection, after checking for LH fault codes, also check the EA/CC/ISC and Distributor Ignition (DI) control unit for fault codes.

Vehicles that use ME fuel injection do NOT have separate DM, EA/CC/ISC or DI control units. These functions have been integrated into the ME control unit. Attempting to access these control units will generate an error message. To verify that a vehicle is equipped with a particular engine system, refer to the MB Engine Management Systems Chart below. Of course, the use of a scanner is required to be able to read all codes from each ECU.

Climate Systems
Many vehicles have climate control systems that can be accessed through the display panel in the passenger compartment. By simply setting the TEMP control wheels and pushing the AUTO function, the complete status of the AC can be determined.

ABS and ASR Systems
Anytime the scanner tool access's the ABS control unit, the ABS warning lamp will illuminate. The light will stay on until the scanner tool is disconnected and the ignition key is cycled.

Online Auto Repair by ALLDATA DIY
The very popular CD-ROM has been discontinued and replaced with an online yearly subscription to ALLDATA DIY for $24.95 that is renewable for $14.95. Since I haven't tried this service I can't recommend it.

Currently, information is available for model years 1982 to 2000. 2001 model year information is scheduled to be released in June/July of 2002. The information available is summarized here:

Factory Recall and Technical Service Bulletins (TSB)
Information that addresses safety, reliability, performance and comfort related problems with your car
Special warranty provisions and extensions.
Fixes for common problems and updated factory repair procedures
Illustrated Diagnosis and Repair Procedures
OEM Part Numbers
Diagnostic Charts and Trouble Codes
Component Locations and Diagrams
Factory Maintenance Schedules


For more info, check out this link: ALLDATA DIY.


MB Engine Management Systems: 140 Chassis S-Class (USA)

My S500 Cpe is highlighted in RED
* VIN letter designations are the 4th through 7th digits of the Vehicle Identification Number.
** Vehicles without a "Check Engine" light do not have a Diagnostic Module (DM).
*** Vehicles with LH fuel injection also have BM, DI and EA control units that store engine codes.

Year Desig VIN* Chassis No Engine Fuel Inj Sys Diag Module**
1992-1993 300SE/S320 GA32 140.032 104 LH*** Yes
1994-1996 S320 GA32 140.032 104 HFM No
1997 S320 GA32 140.032 104 ME2 No
1994-1996 S320 (long) GA33 140.033 104 HFM Yes
1997 S320 (long) GA33 140.033 104 ME2 No
1992 400SE GA42 140.042 119 LH*** Yes
1993-1995 400SEL/S420 GA43 140.043 119 LH*** Yes
1996-1997 S420 GA43 140.043 119 ME1 No
1992-1995 500SEL/S500 GA51 140.051 119 LH*** Yes
1996-1999 S500 GA51 140.051 119 ME1 No
1992-1995 600SEL/S600 GA57 140.057 120 LH*** Yes
1996-1999 S600 GA57 140.057 120 ME1 No
1993-1995 500SEC/S500 Cpe GA70 140.070 119 LH*** Yes
1996-1999 S500/CL500 GA70 140.070 119 ME1 No
1993-1995 600SEC/S600 Cpe GA76 140.076 119 LH*** Yes
1996-1999 S600 Cpe/CL600 GA76 140.076 120 ME1 No


Mercedes Benz Repair Literature (USA)

The following is a list of Diagnostic Manuals of US models gas engine systems. These manuals can be ordered from Mercedes-Benz at 1 (800) 367-6372

STAR Service Manual on DVD for the W140, P-2700-140-04
The W140 DVD covers years 1992 to 1999. It ccontains repair, component disassembly/assembly and parts information. Also contained is the Diagnostic Manual with test and troubleshooting details. The DVD also contains the ETM (Electric Troubleshooting Manual) with STAR finder; great for t/s electrical problems. List price; $87.50

Model line 140 includes 300SE / S320SWB / S320LWB / 400SE / 400SEL / S420 / 500SEL / S500 / 600SEL / S600 / 300SD / S350 / 500SEC / S500 Coupe / 600SEC / S600 Coupe / CL500 / CL600

Volume 1: Test and Adjustment Data for LH, HFM and ME systems
Volume 2: Diagnosis and Repair of LH, HFM and DI systems
Volume 3: Diagnosis and Repair of EA, CC, ISC and DM systems
Volume 4: Diagnosis and Repair of ME systems

Mercedes-Benz Part Number Description
S-2389-CS1 -must have for DIYers! Maintenance Manual for Model Yr '94 and on
S-2489-000 Diag Manual Engines Vol 1 (contents only)
S-2489-S02 Diag Manual Engines Vol 1 Supplement 2
S-2489-S03 Diag Manual Engines Vol 1 Supplement 3
S-2489-S04 Diag Manual Engines Vol 1 Supplement 4
S-2489-S05 Diag Manual Engines Vol 1 Supplement 5
S-2489-S06 Diag Manual Engines Vol 1 Supplement 6
S-2489-S07 Diag Manual Engines Vol 1 Supplement 7
S-2489-S08 Diag Manual Engines Vol 1 Supplement 8
S-2489-S09 Diag Manual Engines Vol 1 Supplement 9
S-2490-000 Diag Manual Engines Vol 2 (contents only)
S-2490-S01 Diag Manual Engines Vol 2 Supplement 1
S-2490-S02 Diag Manual Engines Vol 2 Supplement 2
S-2490-S03 Diag Manual Engines Vol 2 Supplement 3
S-2490-S04 Diag Manual Engines Vol 2 Supplement 4
S-2490-S05 Diag Manual Engines Vol 2 Supplement 5
S-2490-S06 Diag Manual Engines Vol 2 Supplement 6
S-2490-S07 Diag Manual Engines Vol 2 Supplement 7
S-2490-S08 Diag Manual Engines Vol 2 Supplement 8
S-2490-S09 Diag Manual Engines Vol 2 Supplement 9
S-2490-S10 Diag Manual Engines Vol 2 Supplement 10
S-2490-S11 Diag Manual Engines Vol 2 Supplement 11
S-2490-S12 Diag Manual Engines Vol 2 Supplement 12
S-2490-S13 Diag Manual Engines Vol 2 Supplement 13
S-2490-S14 Diag Manual Engines Vol 2 Supplement 14
S-2591-092 Diag Manual Engines Vol 3 (contents only)
S-2591-S01 Diag Manual Engines Vol 3 Supplement 1
S-2591-S02 Diag Manual Engines Vol 3 Supplement 2
S-2591-S03 Diag Manual Engines Vol 3 Supplement 3
S-2591-S04 Diag Manual Engines Vol 3 Supplement 4
S-2591-S05 Diag Manual Engines Vol 3 Supplement 5
S-2591-S06 Diag Manual Engines Vol 3 Supplement 6
S-2591-S07 Diag Manual Engines Vol 3 Supplement 7
S-2591-S08 Diag Manual Engines Vol 3 Supplement 8
S-2638-095 Diag Manual Engines Vol 4 (contents only)
S-2638-S01 Diag Manual Engines Vol 4 Supplement 1
S-2638-S02 Diag Manual Engines Vol 4 Supplement 2
S-2638-S03 Diag Manual Engines Vol 4 Supplement 3
S-2638-S04 Diag Manual Engines Vol 4 Supplement 4
S-2638-S05 Diag Manual Engines Vol 4 Supplement 5
S-2638-S06 Diag Manual Engines Vol 4 Supplement 6


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