Cruise Control - Diagnosis of E-Tempomat System
84mercedes02TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: September, 1984 REF. NO. MBNA 54/10
SUBJECT: E-TEMPOMAT CRUISE CONTROL SYSTEM DIAGNOSIS
The present E-Tempomat (electrically controlled) cruise control system was introduced in model year 1981 (model 126) and is now used in all models. Operational descriptions can be found in the service microfiche or the Model Year 1981 Introduction Manual.
When testing this system, there are two types of problems that may be encountered, each having a different approach of remedy:
A. Functional Problems with System Components
B. Erratic Operation or Poor System Performance
A. Functional Problems with System Components
The test adapter (tool no. 126 589 05 21 00) should be used if it is suspected that a component of the cruise control system is not functioning. If a component functions intermittently (i.e. poor speed regulation or vehicle jerks/surges), the test adapter should not be used. In these cases the steps in Part B should be followed.
NOTE: If a non-functioning part is found during the test with the adapter, all connectors on that part and in that circuit should be checked for good contacts. This includes checking for tight fitting pin sockets and re-tightening them if required. After it has been determined that all electrical connections are good, re-check the part with the tester.
B. Erratic Operation or Poor System Performance - Programmed Repair
Problem:
E-Tempomat cuts out during driving (e.g. due to voltage spikes caused by operation of switchover valves, etc.), but can be reset. All models
Cause:
Voltage spikes in electrical system caused by operating ACC system, switch-over valves, etc.
Remedy:
Install latest version electronic control unit (see S.I. MBNA 54/9)
Problem:
E-Tempomat jerks only when driving downhill. Model 201.024
Cause:
The deceleration fuel shutoff feature of the CIS-E system is not cancelled when driving with the cruise control in operation. Checking is possible by disconnecting the plug of the micro switch (arrow) at the throttle lever. Surging should then be eliminated.
Remedy:
a) Check for continuity between pin 5 of the E-Tempomat control unit and pin 6 of the CIS-E control unit (white wire).
NOTE: If there is no continuity, check the intermediate single pin connector for this white wire located behind the right side footwell kick panel.
b) If point a) is in order, replace CIS-E electronic control unit.
Problem:
E-Tempomat surges only when driving downhill. Model 201.122
Cause:
This complaint is currently under investigation. Replacement of the electronic control unit will not eliminate this problem.
Problem:
E-Tempomat exhibits jerking (not only when driving downhill). This complaint can occur at all times or only in certain speed ranges. Model 201
Cause:
Irregular speed impulses from the sensor (arrow) on the speedometer.
Remedy:
Install new speed sensor with production date 3/84 or later and test drive vehicle.
Problem:
E-Tempomat will not engage at times. AR models
Cause:
Poor electrical contact at the sockets of the plug for the electronic control unit.
Remedy:
Tighten pin sockets together and make sure that the wires are connected to the correct terminal (see ETM).
Problem:
E-Tempomat exhibits jerking. Models 123.133/153/193, starting model year 1982
Cause:
a) Incorrect electronic control unit installed.
b) Accelerator linkage bushing (arrow) not lubricated. Linkage should be pulled by hand through entire operating range to check for excess friction or binding points.
Remedy:
a) Verify that correct electronic control unit is installed (see S.I. MBNA 54/9).
b) Lubricate accelerator linkage. Check fulcrum pin on throttle lever for tight fit, replace throttle lever if necessary.
Problem:
E-Tempomat surges in the entire speed range by approximately 3 to 4 mph. AH models
This can clearly be noticed if the speed has been increased by the use of the control lever. Vehicle will further increase the speed by approx. 3-4 mph after lever is released and then drop back to the set speed again. This fluctuation will continue thereafter.
Cause:
Electronic control mit or wiring defect.
Remedy:
Check wiring harness for shorts. Replace electronic control unit if necessary.
Problem:
E-Tempomat can only be set above a speed of approximately 31 mph. All models
Cause:
a) Verify that correct electronic control unit is installed (See S.I. MBNA 54/9).
b) On vehicles with a ground connection between sockets 14 and 12 of the control unit plug, this connection should be checked for interruption.
Problem:
E-Tempomat actuator rattles after ignition is turned on. AR models
Cause:
Poor connection between wiring harness and E-Tempomat actuator or control unit (2).
Remedy:
a) Check plug connections (1) between wiring harness (arrows) and actuator as well as wiring harness and electronic control unit (2) for tight connections. If required, tighten sockets.
b) Replace cruise control actuator.