1993 Mercedes Benz 300SDFACTORY OEM SERVICE PROCEDURE

Fault Code Definition

After identifying malfunctioning component or system, refer to appropriate 5-CYLINDER FAULT CODE DIAGNOSIS or 6-CYLINDER FAULT CODE DIAGNOSIS charts under DIAGNOSTIC TESTS  .

5-CYLINDER FAULT CODE IDENTIFICATION

Fault Code Component/System Designation
1 (1) All Functions Normal None
2 Fuel Rack Position Sensor L7
3 Airflow Sensor B2/1
4 (2) EDS Control Unit N39
5 (3) EGR Vacuum Transducer Or EGR Valve System Y31/1
6 EDS Control Unit (Internal Power Supply) N39
7 Starter Ring Gear Speed Sensor L3
8 Engine Coolant Sensor B11/4
9 Intake Air Temperature Sensor B2/1a
10 Voltage Supply None
11 (4) ELR Actuator Y22
" Or EGR Vacuum Transducer Y31/1
12 Not Used None
13 EDS Control Unit Defective N39
14 Air Pressure Sensor B5/1
15 Boost Pressure Control/Pressure Control Flap Vacuum Transducer Or Boost Pressure Control Ckt Y31/5
(1) If no fault codes are displayed on pulse counter and driveability or customer complaints are present, perform functional test on ELR, EGR, and P-2 control. See 5-CYLINDER FUNCTIONAL TEST CHARTS  under FUNCTIONAL TESTS.
(2) EDS control unit atmospheric pressure sensor is malfunctioning. Atmospheric pressure sensor is internal to EDS control unit.
(3) Pulse counter will only display at 900 RPM for at least 5 seconds. Fault is not stored.
(4) Pulse counter only displays fault code if a short circuit is present.
6-CYLINDER FAULT CODE IDENTIFICATION

Fault Code Component/System Designation
1 (1) All Functions Normal None
2 Fuel Rack Position Sensor L7
3 Airflow Sensor B2/1
4 (2) EDS Control Unit N39
5 (3) EGR Vacuum Transducer Or EGR Valve System Y31/1
6 EDS Control Unit (Internal Power Supply) N39
7 Engine Speed Sensor L3
8 Engine Coolant Sensor B11/4
9 Intake Air Temperature Sensor B2/1a
10 EDS Control Unit Power Supply N39
11 (4) ELR Actuator Y22
" Or Boost Pressure Cut-Out Switchover Valve Y31/6
" Or EGR Vacuum Transducer Y31/1
12 Not Used None
13 EDS Control Unit Defective N39
14 (5) EDS Pressure Sensor Defective B5/1
15 Boost Pressure Control Vacuum Transducer Or Defect In Boost Pressure Control Ckt Y31/4
(1) If no fault codes are displayed on pulse counter and driveability or customer complaints are present, perform functional test on ELR and EGR. See 6-CYLINDER FUNCTIONAL TEST CHARTS  under FUNCTIONAL TESTS.
(2) EDS control unit atmospheric pressure sensor is malfunctioning. Atmospheric pressure sensor is internal to EDS control unit.
(3) Pulse counter will only display at 900 RPM for at least 5 seconds. Fault is not stored.
(4) Pulse counter only displays fault code if a short circuit is present.
(5) Pressure sensor is located in left rear corner of engine compartment, on firewall.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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