Technical Description of OBD-II Trouble Code
Intermittent Circuit B of Crankshaft Position Sensor
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II (Honda, GMC, Chevrolet, Ford, Volvo, Dodge, Toyota, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
If your vehicle has a stored code P0389, it means that the powertrain control module (PCM) detected an intermittent or erratic voltage signal from the secondary crankshaft position (CKP) sensor. In an OBD II system with multiple CKP sensors, sensor B usually refers to a secondary CKP sensor.
The CKP sensor is responsible for monitoring engine speed (RPM) and crankshaft position. The PCM uses this information to calculate ignition spark timing based on the position of the crankshaft. Since the camshafts rotate at half the speed of the crankshaft, it is crucial for the PCM to distinguish between engine intake and exhaust strokes. The CKP sensor circuitry includes circuits that provide the PCM with an input signal, a 5-volt reference signal, and a ground.
Most CKP sensors are of the electromagnetic, hall-effect type and are typically mounted on the exterior of the engine. They are placed in close proximity to a circuit completing engine ground, usually a reluctor ring with precisely machined teeth attached to either end or integrated into the crankshaft. Some systems with multiple CKP sensors may have a reluctor ring on one end of the crankshaft and another one machined into the center of the crankshaft. Others may mount sensors in multiple positions around a single reluctor ring.
The CKP sensor is positioned so that the reluctor ring passes very close to its magnetic tip as the crankshaft rotates. The raised areas (teeth) of the reluctor ring complete an electromagnetic circuit with the sensor, while the indentations between the raised areas briefly interrupt the circuit. The PCM recognizes these continuous circuit completions and interruptions as a waveform pattern representing voltage fluctuations.
The PCM constantly monitors input signals from the CKP sensors. If the input voltage from the crankshaft position sensor is too low for a certain period of time, a P0389 code will be stored and the malfunction indicator lamp (MIL) may illuminate.
Other trouble codes related to crankshaft position sensor B include P0385, P0386, P0387, and P0388.
Severity of the Code & Symptoms
A stored code P0389 is likely to cause a no-start condition, making it a severe code.
Symptoms associated with this code may include:
Possible Causes
The potential causes for this code to be set are:
Diagnostic and Repair Procedures
Before diagnosing a code P0389, it is necessary to have a diagnostic scanner with an integrated digital volt/ohmmeter (DVOM) and oscilloscope. A reliable source of vehicle information, such as All Data DIY, will also be required.
A visual inspection of all system-related wiring harnesses and connectors is a good starting point for diagnosis. Pay close attention to circuits that have been contaminated with engine oil, coolant, or power steering fluid, as these fluids may compromise the protective insulation on the wiring and lead to shorted or open circuits (resulting in a stored P0389).
If the visual inspection does not yield any results, connect the scanner to the vehicle diagnostic port and retrieve all stored trouble codes and freeze frame data. It can be helpful to write down this information if the P0389 code proves to be intermittent. If possible, test-drive the vehicle to see if the code is reset.
If the P0389 code is reset, locate a system wiring diagram from your vehicle information source and check for voltage at the CKP sensor. Normally, a five-volt reference is used for CKP sensor operation, but refer to the manufacturer’s specifications for the specific vehicle. One or more output circuits and a ground signal should also be present. If reference voltage and ground signals are detected at the CKP sensor connector, proceed to the next step.
Using the DVOM, test the CKP sensor according to the manufacturer’s recommendations. If the CKP sensor resistance levels do not comply with the manufacturer’s specifications, it is likely defective. If the CKP sensor resistance aligns with the manufacturer’s specifications, continue to the next step.
Reconnect the CKP sensor in question and attach the positive test lead of the oscilloscope to the signal output wire. Connect the negative lead to the CKP sensor ground circuit. Turn on the oscilloscope and choose the appropriate voltage setting. Observe the waveform pattern on the oscilloscope while the engine is idling in park or neutral. Look for voltage spikes or glitches in the waveform pattern. If any discrepancies are detected, wiggle-test the wiring harness and connector for the CKP sensor to determine if there is a loose connection or a defective sensor. Excessive metallic debris on the magnetic tip of the CKP sensor or a broken or worn reluctor ring may cause missing voltage blocks in the waveform pattern. If no problems are found in the waveform pattern, proceed to the next step.
Locate the PCM connector and connect the test leads of the oscilloscope to the CKP sensor signal input and ground circuits, respectively. Observe the waveform pattern. If the waveform pattern near the PCM connector is different from what was seen when the test leads were connected near the CKP sensor, suspect an open or shorted circuit between the CKP sensor connector and the PCM connector. If this is the case, disconnect all related controllers and test individual circuits with the DVOM. Repair or replace any shorted or open circuits. If the waveform pattern is identical to what was seen when the test leads were connected near the CKP sensor, the PCM may be defective or there may be a PCM programming error.
Additional diagnostic notes:
