DTC - Erroneous Codes
REF. NO.MBNA 00/48
TO:
OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE:
June 1992
SUBJECT:
MODELS 124.034/036, 140 ERRONEOUS DIAGNOSTIC TROUBLE CODES (DTCS)
The on-board diagnostics introduced with models 124.034/036 and model 140 are intended to enable diagnosis of the vehicle's complex electronically controlled systems. Recent experience has proven that, for the most part, faulty components are being successfully identified. However, some diagnostic trouble codes (DTCS) are generated due to software design shortcomings. Under certain conditions, which are interpreted by the software as implausible, erroneous diagnostic trouble codes may be generated. For example, this can occur when the engine is being started with a very weak battery. As a result, incomplete/distorted information is transmitted to the electronic control modules. In this case, the proper repair would be to recharge the battery. In addition, there are codes which return immediately after having been erased. These are caused by a permanently existing condition (see Antitheft Alarm, code 15, "Comments" section).
Currently, all efforts are being made to identify these types of diagnostic trouble codes and make the necessary software and hardware modifications. The tables list the most frequently reported diagnostic trouble codes, their most likely sources and related comments. The information contained in the tables is based on field experience and reports from Mercedes-Benz AG.
When testing a system, the first course of action should be to consult the Diagnostic Directory for up-to-date DTC information. Then refer to the respective section in the Diagnostic Manual. If no fault could be confirmed, refer to the tables. They may enable quick identification of known erroneous codes and avoid repeat complaints.
However, we must stress that all codes, especially those pertaining to the emission control related Onboard Diagnostic (OBD) system, must be repaired and coded correctly into the warranty system.
In this regard, we wish to inform you of the policy of the California Air Resources Board regarding false malfunction indicator light illumination, i.e. the "CHECK ENGINE" malfunction indicator lamp in our vehicles.
The policy states:
"While the Air Resources Board (ARB) recognizes there may be no direct emission impact due to falsely illuminated malfunction indicator lights (MILs), the ARB is concerned that such MILs will condition owners to ignore the MIL. Thus, when a defect occurs that does affect emissions, vehicle owners will not have it repaired in a timely manner. An illuminated MIL will also cause the vehicle to fail a Smog Check inspection, which may result in additional costs to vehicle owners for repairs that are not needed; if these repairs are performed incorrectly, emissions may actually be increased. We believe that the cost of repairing the defective MIL design should be borne by the manufacturer (which is not necessarily the case in service campaigns) and that all vehicles should be corrected. Therefore, the cases in which the MIL is illuminated incorrectly, the ARB will pursue recalls to correct the cause of the false MIL illumination. These recalls will also be included in the ARB/Department of Motor Vehicles Recall/Registration Renewal Program.
Some manufacturers incorrectly believe that a MIL which falsely illuminates is not an emissions-related problem and, therefore, not subject to the warranty reporting requirements. It is the position of the ARB that all diagnosis and repairs related to the illumination of the MIL are covered by the required emissions warranty. If the diagnosis of a fault code does not produce any specific component failure, it is assumed that the OBD system has itself malfunctioned. This failure of the emission-related OBD system is subject to the warranty reporting regulations."
(Source: MAC 92-02)
This policy must be adhered to regarding "CHECK ENGINE" malfunction indicator lamp illumination in all 50 states.
Erroneous Diagnostic Trouble Codes (DTCS)