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P0389 is a diagnostic trouble code (DTC) for "Crankshaft Position Sensor B Circuit Intermittent". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The powertrain control module (PCM) or another related control module has detected a fluctuation in voltage from the crankshaft position sensor (CPS) B circuit that exceeds the maximum allowable variation from manufacturer’s specs.
The manufacturer’s specs allow a 10 percent variation from predetermined reference voltage on the CPS. Variations of more than 10 percent will cause a trouble code to be stored in the powertrain control module (PCM), illuminating the malfunction indicator lamp (MIL). Some vehicles require as many as three failure cycles to illuminate the MIL; however, a “pending code” will be stored without the MIL being illuminated.
The CPS is a Hall-effect electromagnetic sensor. Some designs use a reluctor ring or teeth attached to the crankshaft, interrupting the field of the electromagnetic sensor and creating a square waveform pattern. These pulses enable the PCM to read the crankshaft position precisely; the PCM uses this information to detect misfires. Engine control systems that use this type of CPS may start and run even with a failure, but performance and fuel economy will be poor. Other designs use the CPS to govern spark timing and ignition control. IN these cases, the CPS failure will usually lead to a no-start condition, stored trouble code and illuminated MIL on the first failure. A good starting point for a successful diagnosis is to check for an engine RPM signal while cranking the engine. This can be done by observing the vehicle’s dashboard tachometer or by using a scanner, depending on the CPS system design.
Timing components should be inspected closely when replacing a broken or worn timing belt, if an engine fails to start afterwards due to a damaged gear, sensor, connector, reluctor ring or wiring. Loose or corroded electrical wiring or connectors are also a possibility.
A P0389 code can result in a vehicle that performs very poorly or won’t start at all.
On vehicles equipped with distributors, the distributor’s Hall-effect sensor, camshaft position sensor and crank position sensor work together to help govern ignition timing and fuel delivery strategies. Engines with multiple camshafts will have multiple CPS sensors. In the event of an intermittent condition, use the oscilloscope to analyze waveforms from the distributor and crank sensors as well, while looking for spikes or glitches in the waveform. These sensors have been known to become contaminated with oil, antifreeze or power steering fluid leaks. Look closely for worn or deteriorated wiring or connectors.
On older vehicles with distributors, test the distributor for slop, end-play and side-to-side wobble along with tests of the sensors.
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