P050B = Cold Start Ignition Timing Performance
The fault code P050b means that the powertrain control module (PCM) has detected a malfunction in the ignition timing control system. Cold start is a term used to describe an engine drivability strategy that is implemented only when the engine is at (or below) ambient temperature.
The PCM calculates ignition timing strategy (including during cold start) using input data received from the crankshaft position (CKP) sensor, the camshaft position (CMP) sensor, the engine temperature sensor (ECT), throttle position sensor (TPS), and the mass airflow (MAF) sensor, among others.
Since OBD-II vehicles are equipped with distributor-less ignition systems, the PCM is programmed 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.
When the engine is cold, timing is advanced slightly to compensate for the lower combustion chamber temperature. In the event that the engine overheats or when knock sensors are activated, ignition timing is retarded by the PCM to prevent engine damage.
If ignition timing cannot be controlled by the PCM, a code P050B will be stored and a malfunction indicator lamp (MIL) may be illuminated.
Some common causes - in the specific order of cost of repair, for this code
Severe vacuum leak.
Open or shorted circuits or connectors
Defective ECT (engine coolant temperature) sensor
Defective CKP or CMP sensor (crankshaft position or camshaft position) sensors.
Diagnose and repair ECT, CKP, or CMP related codes before attempting to diagnose the P050B. When diagnosing a code P050B, I would gain access to a source of reliable vehicle information, a diagnostic scanner with an integrated oscilloscope, and a digital volt/ohmmeter (DVOM).
You'll need the vehicle-specific diagnostic flow charts, wiring diagrams, connector face views, connector pin-out charts, and component testing procedures and specifications to accurately diagnose a code P050B.
1) Perform a visual inspection of all vacuum lines and hoses, wiring harnesses, and related connectors. If the CKP or CMP sensor connectors are contaminated with oil these should be cleaned or replaced (sensor and connector).