What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles (Honda, GMC, Chevrolet, Ford, Volvo, Dodge, Toyota, etc.). Although generic, the specific repair steps may vary by make/model.
If your vehicle has a stored P0389 code, it means the Powertrain Control Module (PCM) has detected an intermittent or erratic voltage signal from the secondary crankshaft position sensor (CKP). When an OBD II system uses multiple CKP sensors, the B sensor typically refers to a secondary CKP sensor.
Engine speed (RPM) and crankshaft position are monitored using the CKP sensor. The PCM calculates ignition spark timing using the crankshaft position. When you consider that camshafts rotate at half the speed of the crankshaft, you see why it is so important for the PCM to be able to distinguish between the engine’s intake and exhaust strokes (rotations). The CKP sensor circuit includes one or more dedicated circuits to provide the PCM with an input signal, a 5-volt reference signal, and a ground.
CKP sensors are most often electromagnetic, Hall effect variety. They are usually mounted on the outside of the engine and placed in very close proximity (usually only a few thousandths of an inch) to a circuit completing the engine ground. The engine ground is typically a reluctor ring (with precision-machined teeth) attached to either end of the crankshaft or integrated into the crankshaft itself. Some systems with multiple CKP sensors may use a reluctor ring at one end of the crankshaft and another machined at the center of the crankshaft. Others will simply mount sensors in multiple positions around a single reluctor ring.
The CKP sensor is mounted so that the reluctor ring passes within a few thousandths of an inch of its magnetic tip as the crankshaft rotates. The raised areas (teeth) of the reluctor ring complete an electromagnetic circuit with the sensor, and 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 variations.
The input signals from the CKP sensors are constantly monitored by the PCM. If the input voltage from the crankshaft position sensor is too low over a defined period, a P0389 code will be stored and the MIL may be illuminated.
Other B crankshaft position sensor fault codes include P0385, P0386, P0387, and P0388.
Code Severity and Symptoms
A no-start condition will likely accompany a stored P0389 code. Therefore, this code could be classified as severe.
Symptoms of this code may include:
Engine will not start
Tachometer (if applicable) does not register RPM when the engine is cranked
Hesitation during acceleration
Poor engine performance
Reduced fuel economy
Causes
Possible causes for this code being set are:
Faulty CKP sensor
Open or shorted wiring to the CKP sensor
Corroded or fluid-soaked connector at the CKP sensor
PCM programming error or faulty PCM
Diagnostic and Repair Procedures
You will need a diagnostic scanner, along with a digital volt/ohmmeter (DVOM) and an oscilloscope, before diagnosing a P0389 code. A reliable source of vehicle information, such as All Data DIY, will also be required.
A visual inspection of all wiring harnesses and connectors related to the system is a good place to start your diagnosis. Circuits that have been contaminated by engine oil, coolant, or power steering fluid should be inspected carefully, as petroleum-based fluids can compromise the protective insulation on wiring and lead to short or open circuits (and a stored P0389).
If the visual inspection yields no results, connect the scanner to the vehicle’s diagnostic port and retrieve all stored fault codes and freeze frame data. Writing down this information may prove useful if the P0389 proves to be intermittent. If possible, test drive the vehicle to see if the code resets.
If the P0389 resets, find a wiring diagram for the system from your vehicle information source and check the voltage at the CKP sensor. A five-volt reference is normally used for CKP sensor operation, but check the manufacturer’s specifications for the vehicle in question. One or more output circuits and a ground signal will also be present. If the reference voltage and ground signals are detected at the CKP sensor connector, proceed to the next step.
Using the DVOM, test the CKP sensor in question according to the manufacturer’s recommendations. If the CKP sensor’s resistance levels are not within the manufacturer’s recommendations, suspect it is faulty. If the CKP sensor’s resistance matches the manufacturer’s specifications, proceed to the next step.
Attach the oscilloscope’s positive test lead to the signal output wire and connect the negative lead to the CKP sensor’s ground circuit after reconnecting the CKP sensor in question. Choose the appropriate voltage setting on the oscilloscope and turn it on. Observe the waveform pattern on the oscilloscope with the engine idling in Park or Neutral. Monitor for voltage spikes or glitches in the waveform pattern. If anomalies are detected, test the wiring harness and connector (for the CKP sensor) to determine if the issue is a loose connection or a faulty sensor. If the magnetic tip of the CKP sensor contains excessive metal debris or if there is a broken or worn reluctor ring, this can cause missing voltage blocks in the waveform pattern. Proceed to the next step if no issues are found in the waveform pattern.
Locate the PCM connector and insert the oscilloscope test leads into the CKP sensor input signal 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 associated controllers and test the individual circuits with the DVOM. You will need to repair or replace any shorted or open circuits. The PCM may be faulty, or you may have a PCM programming error, if the waveform pattern is identical to what was seen when the test leads were connected near the CKP sensor.
Additional Diagnostic Notes:
Some manufacturers recommend replacing CKP and CMP sensors as a set
Use technical service bulletins to assist in the diagnostic process