Technical Description of OBD-II Trouble Code
Performance Issue with Cold Start Ignition Timing
What is the meaning of this?
This generic powertrain diagnostic trouble code (DTC) is commonly found in many OBD-II vehicles, including those from Jeep, Jaguar, Dodge, BMW, Land Rover, Toyota, VW, Ford, Mitsubishi, Mazda, etc.
If your OBD-II vehicle has stored a code P050B, it indicates that the powertrain control module (PCM) has detected a malfunction in the ignition timing control system. Cold start refers to an engine drivability strategy that is only implemented when the engine is at or below the ambient temperature.
The PCM calculates the ignition timing strategy, including during cold start, using input data from various sensors such as the crankshaft position (CKP) sensor, camshaft position (CMP) sensor, engine temperature sensor (ECT), throttle position sensor (TPS), and mass airflow (MAF) sensor.
Since OBD-II vehicles have distributor-less ignition systems, the PCM is programmed to deliver a base timing strategy and adjust the ignition timing as needed. Changes in engine load and RPM require different degrees of ignition timing to optimize engine performance and fuel efficiency.
When the engine is cold, the timing is slightly advanced to compensate for the lower combustion chamber temperature. If the engine overheats or knock sensors are activated, the PCM retards the ignition timing to prevent engine damage.
If the PCM is unable to control the ignition timing, a code P050B will be stored and the malfunction indicator lamp (MIL) may illuminate. Most vehicles will require multiple ignition cycles with a failure for the MIL to illuminate.
Cold car:
What is the severity of this DTC?
Incorrect ignition timing can lead to catalytic converter damage, poor engine performance, and reduced fuel efficiency. A code P050B should be considered severe and addressed promptly.
What are some of the symptoms of the code?
Symptoms of a P050B engine code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P050B troubleshooting steps?
Prioritize diagnosing and repairing ECT, CKP, or CMP related codes before attempting to diagnose the P050B.
When diagnosing a code P050B, it is recommended to have access to reliable vehicle information, a diagnostic scanner with an integrated oscilloscope, and a digital volt/ohmmeter (DVOM).
You will need diagnostic flow charts, wiring diagrams, connector face views, connector pin-out charts, and component testing procedures and specifications to accurately diagnose a code P050B. This information can be found in your source of vehicle information.
Note: We are aware of a few technical bulletins issued by manufacturers. For example, one is for Jeep, #18-011-13, and one for Jaguar #XJ303-014 specific to this P050B diagnostic code.
Conduct a visual inspection of all vacuum lines and hoses, wiring harnesses, and related connectors. Clean or replace CKP or CMP sensor connectors that are contaminated with oil (both the sensor and connector).
Connect the oscilloscope (as described below) and prepare for a cold engine start. Ensure that the scope test leads are routed away from moving parts.
Test the CKP and CMP sensors using the oscilloscope:
If no waveform pattern is displayed on the oscilloscope, test CKP and CMP sensor reference voltage and ground:
If no reference voltage is detected, use the DVOM (and the battery) to determine whether the reference or the ground is inadequate. If there is no reference voltage, use the test lead of the DVOM to probe the corresponding circuit at the PCM connector. If no reference voltage is discovered there, suspect a PCM problem. If there is reference voltage at the PCM and none at the sensor, there may be an open circuit.
If there is no ground, trace it back to its source and ensure that it is secure. In some cases, it may be necessary to install an auxiliary ground.
Use the DVOM to test CKP and CMP sensors:
