Mercedes C280 Diagnostic Codes with an LED and pushbutton.

NOTE: This repair was done on my 1994 C280. However it may work for other years/models. I cannot guarantee 100% accuracy nor can I be liable for any damage one can cause to his or her car or self.

This diagnostic mode works on my 1994 C280. It should work on 1994-1997 models, but I can't guarantee it.


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| Read Codes | HFM/SFI ECU Codes | CC/ISC Codes (without ASR) | EA/CC/ISC Codes (with ASR) |

The unit will connect to the underhood 38 pin diagnostic connector. When activated, the LED will flash a number of times which will correllate to a trouble code. Here are the parts needed to build your own tester. You also need a soldering iron if you want any of the components to stay put.

Here is a schematic of how the unit will be wired:

Here is a more visual diagram to the connections. Note, the long leg of the LED is the positive lead.

Finally, here is a view of the diagnostic connector with labeled pins


Using the Code Reader


Code lookup tables

HFM/SFI ECU Codes

DTC Possible Cause
1 No Malfunction in system
2 Engine Coolant Temperature Sensor: Short Circuit
Engine Coolant Temperature Sensor: Open Circuit
Engine Coolant Temperature Sensor: Implausible Reading
Engine Coolant Temperature Sensor: Intermittent Contact
3 Intake Air Temperature Sensor: Short Circuit
Intake Air Temperature Sensor: Open Circuit
Intake Air Temperature Sensor: Intermittent Contact
4 Mass Air Flow Meter: Air Flow Implausibly High
Mass Air Flow Meter: Open Circuit
5 Throttle Position Switch: Throttle Valve Angle Implausibly High
Throttle Position Switch: Air Flow Implausibly High
Throttle Position Switch: Intermittent Contact
8 Idle Speed Control System: Lower Control Stop
Idle Speed Control System: Upper Control Stop
Cruise Controller or Electronic Throttle Actuator in "Limp-Home" Mode
9 Oxygen Sensor 1 (Before Catalytic Converter): Sensor Voltage Too High
Oxygen Sensor 1 (Before Catalytic Converter): Cold or Open Circuit
Oxygen Sensor 1 (Before Catalytic Converter): Sensor Voltage Implausible
10 Oxygen Sensor 2 (After Catalytic Converter): Sensor Voltage Too High
Oxygen Sensor 2 (After Catalytic Converter): Cold or Open Circuit
Oxygen Sensor 2 (After Catalytic Converter): Sensor Voltage Implausible
11 Oxygen Sensor 1 Heater(Before Catalytic Converter): Current too High
Oxygen Sensor 1 Heater (Before Catalytic Converter): Current too Low
Oxygen Sensor 1 Heater (Before Catalytic Converter): Short Circuit
12 Oxygen Sensor 2 Heater (After Catalytic Converter): Current too High
Oxygen Sensor 2 Heater(After Catalytic Converter): Current too Low
Oxygen Sensor 2 Heater (After Catalytic Converter): Short Circuit
13 Oxygen Sensor System: Operating at Rich Limit, Mixture Too Lean
Oxygen Sensor System: Operating at Lean Limit, Mixture Too Rich
14 Injector Cylinder 1: Short Circuit to Positive
Injector Cylinder 1: Open/Short Circuit to Ground
15 Injector Cylinder 2: Short Circuit to Positive
Injector Cylinder 2: Open/Short Circuit to Ground
16 Injector Cylinder 3: Short Circuit to Positive
Injector Cylinder 3: Open/Short Circuit to Ground
17 Injector Cylinder 4: Short Circuit to Positive
Injector Cylinder 4: Open/Short Circuit to Ground
18 Injector Cylinder 5: Short Circuit to Positive
Injector Cylinder 5: Open/Short Circuit to Ground
19 Injector Cylinder 6: Short Circuit to Positive
Injector Cylinder 6: Open/Short Circuit to Ground
20 Adaptation at Idle: Too Rich
Adaptation at Idle: Too Lean
Adaptation at Lower Partial Load: Too Rich
Adaptation at Lower Partial Load: Too Lean
Adaptation at Upper Partial Load: Too Rich
Adaptation at Upper Partial Load: Too Lean
21 Ignition Output 3 or Ignition Coil 3 for Cylinder 1: Misfire
Ignition Output 3 or Ignition Coil 3 for Cylinder 6: Misfire
Ignition Output 3 or Ignition Coil 3: Current Value Not Obtained
22 Ignition Output 1 or Ignition Coil 1 for Cylinder 2: Misfire
Ignition Output 1 or Ignition Coil 1 for Cylinder 5: Misfire
Ignition Output 1 or Ignition Coil 1: Current Value Not Obtained
23 Ignition Output 2 or Ignition Coil 2 for Cylinder 3: Misfire
Ignition Output 2 or Ignition Coil 2 for Cylinder 4: Misfire
Ignition Output 2 or Ignition Coil 2: Current Value Not Obtained
24 Crankshaft Position Sensor: Signal Not Recognized/Implausible
Crankshaft Position Sensor: Magnet is Missing (segment control)
Crankshaft Position Sensor: Number of Teeh Implausible (increment control)
Crankshaft Position Sensor: RPM Implausibly High
25 Camshaft Position Sensor: Signal Not Recognized/Implausible (segment control)
Camshaft Hall-effect Sensor: Signal Not Recognized/Implausible (increment control)
27 RPM Signal Output: Short Circuit to Ground
RPM Signal Output: Short Circuit to Positive
28 Vehicle Speed Sensor: Signal Not Recognized
Vehicle Speed Sensor: Signal Implausibly High
30 Fuel Pump Relay Module: Open/Short Circuit
32 Knock Sensor 1: Open Circuit
Knock Sensor 2: Open Circuit
33 Maximum retard setting on at least one cylinder has been reached.
Ignition angle deviation between the individual cylinders is > 6° crankshaft angle.
34 Knock Control Evaluation Circuit in Engine Control Module: Defective
35 AIR Pump Switchover Valve and/or AIR relay module: Open/Short Circuit
36 Purge Control Valve: Open/Short Circuit
Purge Control Valve: Short Circuit to Positive
37 Upshift Delay Switchover Valve: Open/Short Circuit
38 Adjustable Camshaft Timing Solenoid: Short Circuit to Positive
Adjustable Camshaft Timing Solenoid: Open/Short Circuit to Ground
39 EGR Switchover Valve: Short Circuit to Positive
EGR Switchover Valve: Open/Short Circuit to Ground
40 Transmission Overload Protection Switch: Short Circuit to Ground
Transmission Overload Protection Switch: Closed and 2nd Gear Recognized
Transmission Overload Protection Switch: Open and 2nd Gear Recognized
Transmission Overload Protection Switch: Implausible
41 CAN Communication from Engine Control Module: Defective
42 CAN Communication from ASR Control Module: Defective
CAN Communication from EA/CC/ISC Control Module or CC/ISC Control Module: Defective
CAN Communication from Diagnostive Module (OBD-II): Defective
43 Starter Signal Not Present
45 Fuel Safety Shut-Off of Electronic Accelerator or Cruise Control: Active
46 Resonance Intake Manifold Switchover Valve: Short Circuit to Positive
Resonance Intake Manifold Switchover Valve: Open/Short Circuit to Ground
48 Oxygen Sensor 2 (After Catalytic Converter) Heater Relay Module: Short Circuit to Positive
Oxygen Sensor 2 (After Catalytic Converter) Heater Relay Module: Open/Short Circuit to Ground
49 Voltage Supply Circuit at Engine Control Module: Implausible
Voltage Supply Circuit at Engine Control Module: Low Voltage
49 Engine Control Module


Cruise Control/Idle Speed Control Computer Codes (models without ASR/traction control)

DTC Possible Cause
1 No Malfunction in system
2 CC/ISC Control Module
Closed Throttle Position Switch
Stop Lamp Switch
Cruise Control Switch (OFF)
Actual Value Potentiometer
Starter Lock-Out/Backup Lamp Switch
Engine Speed Signal
Vehicle Speed Signal
Safety Relay Within CC/ISC Control Module
Engine Wiring Harness
3 CC/ISC Actuator
Throttle Valve Actual Value Potentiometer
Drive Actual Value Potentiometer
Safety Contact Switch
Closed Throttle Position Switch Recognition
Potentiometer Voltage Supply
Reset Not Accomplished (Actuator Adaptation)
4 Cruise Control Switch
5 Stop Lamp Switch
7 CAN Databus:
Message from CC/ISC Control Module: Faulty
Reception from Engine Control Module: Faulty
8 Left Front Axle Vehicle Speed Sensor from ABS or ETS/SPS Control Module
9 Rear Axle Vehicle Speed Sensor from ABS Control Module
Left Rear Axle Vehicle Speed Sensor from ETS/SPS Control Module
Incorrect CC/ISC Control Module Installed
ETS Signal
10 Engine Speed Signal from Engine Control Module
11 Fuel Safety Shut-Off Signal to Engine Control Module


Electronic Throttle Actuator/Cruise Control/Idle Speed Control Computer Codes (models with ASR/traction control)

DTC Possible Cause
1 No Malfunction in system
2 EA/CC/ISC Control Module
Safety Contact Switch
Stop Lamp Switch
Cruise Control Switch (OFF)
Actual Value Potentiometer
Starter Lock-Out/Backup Lamp Switch
Closed Throttle Position Switch
Engine Speed Signal
Vehicle Speed Signal
Safety Relay Within CC/ISC Control Module
Engine Wiring Harness
3 EA/CC/ISC Actuator
Reference Potentiometer (Voltage Supply) Reference Potentiometer Actual Value Potentiometer
Safety Contact Switch
Closed Throttle Position Switch
Actuator Motor
Magnetic Clutch
Reset Not Accomplished (Actuator Adaptation)
4 Cruise Control Switch
5 Stop Lamp Switch
6 Starter Lock-Out/Backup Lamp Switch
7 CAN Databus:
Message from EA/CC/ISC Control Module: Faulty
Reception from Engine Control Module: Faulty
8 Left Front Axle Vehicle Speed Sensor from ASR Control Module
9 Left Rear Axle Vehicle Speed Sensor from ASR Control Module
10 Engine Speed Signal from Engine Control Module
11 Fuel Safety Shut-Off Signal to Engine Control Module
Closed Throttle Recognition Signal to Engine Control Module
14 Closed Throttle Position
15 CAN Databus: Data exchange with ASR control module implausible

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© Copyright. Martin Kosonen. 2010.