P0389 Crankshaft Position Sensor B Circuit Malfunction

OBD-II DTC Datasheet

Crankshaft Position Sensor B Circuit Malfunction

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles (Honda, GMC, Chevrolet, Ford, Volvo, Dodge, Toyota, etc.). Although general in nature, the specific repair steps may differ depending on the brand / model.

If your vehicle has a stored code P0389, it means the powertrain control module (PCM) has detected an intermittent or intermittent voltage signal from the secondary crankshaft position (CKP) sensor. When multiple CKP sensors are used in the OBD II system, sensor B is usually referred to as the secondary CKP sensor.

Engine speed (rpm) and crankshaft position are monitored by the CKP sensor. The PCM calculates the ignition timing using the position of the crankshaft. When you consider that the camshafts rotate at half crankshaft speed, you can see why it is so important that the PCM can distinguish between engine intake and exhaust (RPM) strokes. The CKP sensor circuitry includes one or more circuits to provide an input signal, a 5V reference, and a ground to the PCM.

CKP sensors are most often electromagnetic Hall effect sensors. They are usually mounted external to the motor and placed in close proximity (usually only a few thousandths of an inch) to the motor ground circuit. The engine ground is usually a reaction ring (with precision machined teeth) attached to either end of the crankshaft or built into the crankshaft itself. Some systems with multiple crankshaft position sensors may use a reaction ring at one end of the crankshaft and the other at the center of the crankshaft. Others simply install sensors in multiple positions around a single ring of the reactor.

The CKP sensor is mounted so that the reactor ring extends within a few thousandths of an inch of its magnetic tip as the crankshaft rotates. The protruding parts (teeth) of the reactor ring close the electromagnetic circuit with the sensor, and the recesses between the protrusions briefly interrupt the circuit. The PCM recognizes these continuous shorts and interruptions as a waveform pattern representing voltage fluctuations.

The input signals from the CKP sensors are constantly monitored by the PCM. If the input voltage to the CKP sensor is too low for a specified period of time, a P0389 code will be stored and the MIL may illuminate.

Other CKP Sensor B DTCs include P0385, P0386, P0387, and P0388.

Code severity and symptoms

A no start condition is most likely to accompany a stored P0389 code. Therefore, this code can be classified as serious.

Symptoms of this code may include:

The engine will not start
The tachometer (if equipped) does not register the RPM when the engine is cranking.
Oscillation on acceleration
Poor engine performance
Reduced fuel efficiency

reasons

Possible reasons for setting this code:

Defective CKP sensor
Open or short circuit in the wiring of the CKP sensor
Corroded or liquid-soaked connector on the CKP sensor
Faulty PCM or PCM programming error

Diagnostic and repair procedures

I will need a diagnostic scanner with a built-in digital volt / ohmmeter (DVOM) and oscilloscope before diagnosing the P0389 code. You will also need a reliable source of vehicle information such as All Data DIY.

A visual inspection of all system-related wiring harnesses and connectors is a good place to start diagnosing. Circuits contaminated with engine oil, coolant, or power steering fluid should be carefully inspected as petroleum-based fluids can compromise wire insulation and cause shorts or open circuits (and a stored P0389).

If visual inspection fails, connect the scanner to the vehicle's diagnostic port and retrieve all stored DTCs and freeze frame data. Recording this information can be helpful if P0389 is found to be unstable. If possible, test drive the vehicle to make sure the code has been cleared.

If P0389 is reset, find the system wiring diagram from the vehicle information source and check the voltage at the CKP sensor. The reference voltage is usually used for the operation of the CKP sensor, 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 reference voltage and ground signals are found at the CKP sensor connector, go to the next step.

Using the DVOM, test the CKP in question according to the manufacturer's recommendations. If the resistance levels of the CKP sensor are not in accordance with the manufacturer's recommendations, suspect that it is defective. If the resistance of the CKP sensor matches the manufacturer's specifications, proceed to the next step.

Connect the positive test lead of the oscilloscope to the signal output lead and the negative lead to the ground circuit of the CKP sensor after reconnecting the corresponding CKP sensor. Select the appropriate voltage setting on the oscilloscope and turn it on. Observe the waveform on the oscilloscope with the engine idling, park or neutral. Watch out for power surges or waveform faults. If any mismatches are found, test the harness and connector (for the CKP sensor) to determine if the problem is a loose connection or a faulty sensor. If there is an excessive amount of metal debris on the magnetic tip of the CKP sensor, or if there is a broken or worn reflector ring, this may result in the absence of voltage blocks in the waveform pattern. If no problem is found in the waveform pattern, proceed to the next step.

Locate the PCM connector and insert the oscilloscope test leads into the CKP sensor signal input and ground circuits, respectively. Observe the waveform. If the waveform sample near the PCM connector is different from what was seen when the test leads were connected near the CKP sensor, suspect an open or short circuit between the CKP sensor connector and the PCM connector. If true, disconnect all related controllers and check individual circuits with DVOM. You will need to repair or replace open or closed circuits. The PCM may be defective, 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 the CKP and CMP sensors as part of the kit.
Use service bulletins to assist with the diagnostic process

Related DTC discussions

2005 Acura changed timing belt, P0389I replaced the timing belt and water pump only to have the engine and VSA lights come on (both "VSA" and "!"). The code is P0389. I tried to reset the settings, but immediately pops up. Checked all the timing marks and everything looks good. Could you give some good advice please!!!…

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