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.

Return to 202Tech How-Tos

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.

An LED

A Resistor (1000 to 3000ohms should work)

Momentary Push-button

Some wire (Preferably different colors if you have it laying around)

Something thin enough to be inserted into the pin sockets that can be soldered to the end of the wire. If your wire is thin enough, you may be able to insert it into the sockets alone, otherwise, just some thin solid copper wire would also work.f

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

To use the code reader, first connect the ground wire to pin 1, +12v to pin 3 and the diagnostic wire to either pin 4 or 7 depending on whether you want to diagnose the Engine Control Module or Electronic Accelerator/Cruise Control/Idle Speed Controller Module.

At this point the LED should not be lit up. Turn on the ignition. To activate the diagnostics, press the pushbutton for 2 - 4 seconds. Note, when the button is pressed the LED will light up.

Right after you press the button the LED will begin to flash. It will flash for 0.5 seconds and pause for 1 second between each digit. The number of flashes correllates to the diagnostic code which you can look up below.

Once the first code is read, you may wish to delete the code. To delete it, wait 3 seconds after the LED is finished flashing and press the button for 6-8 seconds. Note, Each code must be erased individually.

Further codes can be read by pressing the button for 2-4 seconds again.

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