Error Code P050B is defined as Cold Start Ignition Timing Performance. This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system or vehicles made since 1996 up to present. This includes vehicles from but not limited to BMW, Dodge, Ford, Jaguar, Jeep, Land Rover, Mazda, Mitsubishi, Volkswagen, etc. Specifications on the definition, troubleshooting, and performance, of course, vary from one make and model to another.
If the vehicle stores this code, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has determined a problem in the vehicle’s ignition timing control system. The term ‘Cold Start’ is used to describe the engine’s drivability strategy that is used only when the engine at (or below) the ambient temperature.
Using the input data it receives from the CKP (crankshaft position) sensor, CMP (camshaft position) sensor, the engine temperature sensor (ECT), throttle position sensor (TPS), and the mass airflow (MAF) sensor, and others, the PCM calculates the timing strategy (including during cold start).
OBD-II vehicles come with a distributor-less ignition system, thus the PCM is tasked to deliver a base timing strategy and to advance and retard ignition timing as required. Changes in engine load and RPM demand varying degrees of ignition timing to help optimize engine performance and maximize fuel efficiency.
To compensate for the lower combustion chamber temperature during cold season (when the engine is cold) timing is advanced slightly. In the event that the engine overheats or when knock sensors are activated, the ignition timing is retarded by the PCM to prevent engine damage.
If the PCM can no longer control the ignition timing, then the Error Code P050B will be stored, activating the Check Engine light. For most vehicles, it will require multiple ignition cycle failures to activate the Check Engine light.
- Excessively rich exhaust
- Engine stalls at idle
- Pinging noise upon acceleration
Other CKP or CMP sensor related codes may be present.
- Severe vacuum leak
- Defective ECT sensor
- Open or shorted circuits or connectors
- Bad CKP or CMP sensor
How to Check
If there are other ECT, CKP, or CMP related codes other than the Error Code P0508, then they should be addressed first.
When diagnosing this code, it is important to refer to a reliable vehicle information source, diagnostic scanner with an integrated oscilloscope, and a DVOM (digital volt/ohmmeter.)
Check the diagnostic flow charts, connector face views, connector pin-out charts, wiring diagrams, and component testing procedures and specifications to diagnose this code. You can find this information from the vehicle information source.
Then conduct a thorough visual inspection of all the vacuum lines and hoses, wiring harnesses, and other related connectors. Clean or replace CKP or CMP sensor or connectors that are contaminated with oil.
Then, connect the oscilloscope and prepare to initiate a cold engine start. Make sure you route the scope test leads away from the moving parts.
Next, test the CKP and CMP sensors using the oscilloscope:
- Start by probing the signal circuit of the sensor with the positive test lead of the scope
- Connect the negative test lead to the sensor ground wire
- The reference voltage of CKP and CMP sensor is typically at 5V. Choose the appropriate voltage setting on the scope
- Start the engine and observe the waveform pattern on the scope display
- There should be an even waveform pattern with no voltage spikes or glitches at all RPM levels
- Suspect sensor failure or a poor electrical connection if there are inconsistencies in the waveform pattern
If you see no waveform pattern displayed on the oscilloscope, test CKP and CMP sensor reference voltage and ground:
- Proceed by probing the reference circuit pin of the sensor connector using positive test lead of the DVOM. The key should be on with the engine off (KOEO) and the sensor disconnected
- Use the negative test lead of the DVOM to probe the ground pin of the same connector
- Reference voltage must be within specifications (usually 5-volts)
If you don’t see voltage reference, then use the DVOM (and the battery) to find out whether the reference or the ground is inadequate. If no reference voltage still, then 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, you have an open circuit.
If there is no ground, trace it back to its source and make sure that it is secure. Sometimes it is better to install an auxiliary ground.
Use the DVOM to test CKP and CMP sensors:
- With the Key On Engine Off, set DVOM at ohms and unplug the sensor connector
- Then, probe the pins in each sensor using the test leads
- Compare your findings with sensor testing specifications
- Sensors which do not comply with specs are faulty
- Applicable technical service bulletins (TSB) will help you reach an accurate diagnosis
How to Fix
Depending on the diagnosis, common repairs for this code are:
- Repair or replace vacuum leak
- Repair or replace ECT sensor
- Repair or replace open or shorted circuits or connectors
- Replace CKP or CMP sensor
Wrong ignition timing may contribute to poor engine performance, damage to the catalytic converter, and increase in fuel consumption. Thus, this code should be considered severe and must be addressed as soon as possible.