A 2006 Mercedes-Benz E-Class W211 rolled in with a glow plug light staying on and a cluster of pedal correlation codes. The vehicle, operating in the Italian market, logged five distinct fault codes: P2136, P2231, P2137, P2299, and P2270. What looks like a tangled mess of electrical issues is actually a clear set of three independent failures, each requiring its own diagnostic path.
Isolating the Accelerator Pedal Faults
Our diagnostic platform analyzed the codes and ranked a defective accelerator pedal module as the most critical issue, assigning it a 90 percent likelihood. The codes P2136 and P2137 are correlation errors between the internal sensors (tracks A/C and B/C) inside the pedal assembly. Modern drive-by-wire systems use redundant potentiometer tracks for safety. When the voltage sweeps from these tracks do not match, the engine control unit refuses to trust the driver's input.
This discrepancy triggers a high severity failure, usually forcing the vehicle into a strict limp mode. Furthermore, code P2299 indicates an incompatibility between the brake pedal and the accelerator pedal signals. While this can sometimes happen if a driver rests their left foot on the brake, seeing it alongside P2136 and P2137 strongly points to a physical defect in the pedal module's internal sliding contact tracks.
Before ordering a replacement pedal, the platform also highlighted a 70 percent probability of wiring problems causing these exact codes. The W211 chassis is known for moisture accumulation and subsequent corrosion in the footwell area. A loose connection or water ingress at the pedal harness can cause the intermittent voltage drops that trigger correlation faults. The suggested diagnostic steps are straightforward. A technician must check the supply voltage directly at the pedal connector and monitor the accelerator pedal values via a live data stream to look for dropouts. A thorough visual inspection of the pedal connector and a continuity test of the signal lines are mandatory before condemning the pedal module itself.
Tracing the Oxygen Sensor Heater Circuit
Moving away from the driver's footwell, the vehicle also presented codes P2231 and P2270. The engine ranked a failure of the pre-catalytic converter oxygen sensor heater circuit at an 85 percent likelihood with a medium severity. Code P2231 points directly to a problem in the pulse width modulated heater circuit for this sensor.
Oxygen sensors must reach a specific operating temperature to generate accurate voltage readings. Because exhaust gases alone do not always keep the sensor hot enough, especially at idle or during warm-up, the integrated heater is critical. When the heater fails, the sensor stays cold and delivers inaccurate data. This manifests as code P2270, which means the oxygen sensor signal is biased or stuck lean.
This is a significant problem for modern diesel engines because a stuck lean signal disrupts exhaust gas management and can actively prevent diesel particulate filter regeneration. The recommended testing path requires measuring the resistance of the oxygen sensor heater circuit to see if the internal element is open. This must be followed by a visual inspection of the oxygen sensor wiring harness to rule out chafing or heat damage near the exhaust system.
Addressing the Glow Plug Indicator
The technician who scanned this vehicle provided one crucial piece of context, noting verbatim that the glow plug lamp often stays on after engine start. The platform took this symptom and ranked a defective glow plug control module or individual faulty glow plugs at an 80 percent likelihood.
This is a remarkably common scenario on OM642 engines. When the glow plug control module detects an open circuit or excess resistance on one of the glow plug circuits, it commands the dashboard indicator to remain illuminated after the engine is running. This serves as a direct warning to the driver. The root cause is typically either a failed solid-state glow plug control module or one or more burnt-out glow plugs.
A failure here leads to difficult cold starts and increased emissions before the engine reaches operating temperature. To confirm the exact point of failure, the technician needs to read the fault memory specifically from the glow plug control module. Following that, running a simple resistance check on the individual glow plugs will reveal which cylinders have failed components and whether the module itself needs to be replaced.
Structuring the Repair Order
When a vehicle presents multiple isolated faults like this W211, prioritizing the repair order is essential for workshop flow. The accelerator pedal module demands immediate attention because it directly affects the vehicle's drivability and safety. Once the pedal voltage supply is verified and the component is repaired, the technician can address the oxygen sensor heater to restore proper emissions control and DPF regeneration. Finally, the glow plug circuit can be tested and resolved. If you frequently see OM642 engines with prolonged glow plug indicators, I am interested to hear if you usually find the module or the plugs to be the primary culprit.