|Code||Fault Location||Probable Cause|
|P0389|| Crankshaft position (CKP) sensor B -circuit intermittent |
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|Wiring, poor connection, CKP sensor, ECM|
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What Does Code P0389 Mean?
Inside your engine, a complex ballet of fuel and fire is being performed. At 2,000 rpm, each spark plug fires 1,000 times, or once every 60 milliseconds. Also, every 60 ms, the fuel injectors deliver a pulse of precisely metered fuel, usually somewhere between one and four milliseconds long. Additionally, vehicles equipped with variable valve timing (VVT) need to vary intake and exhaust timing, as well as lift in some cases, depending on engine speed and load.
Obviously, timing is everything and, in the modern engine, timing down to the millisecond is absolutely essential for proper operation, power delivery, and fuel economy. Regarding the most basic timing in an engine, the engine control unit (ECU) monitors the crankshaft position sensor, often abbreviated as CKP. The CKP sensor reacts to a toothed wheel on the crankshaft, generating a signal, which the ECU used to determine two very important data points – engine speed (RPM) and engine position, or cylinder #1 top dead center (TDC). Using this information, the ECU modulates all other engine functions.
What are the common causes of code P0389 ?
Depending on year, make, and model, DTC P0389 may have number of causes, pretty much the same as those causing DTCs P0385, P0340 or P0345:
- Faulty Sensor – If the sensor is open or shorted, due to age, damage, or corrosion, a weak signal or no signal will be generated.
- Poor Installation – A good CKP signal is highly dependent on sensor placement. Generally, the sensor needs between 0.020” and 0.050” clearance to the reluctor ring. If the sensor is cocked to one side or not firmly seated, the clearance will be wrong and the signal will be too weak for the ECU to detect. If the reluctor ring is rubbing the sensor, the signal will be distorted.
- Ford Trucks / Mustang GT – An alternator phase problem, such as a blown diode or open coil, may cause so much electrical interference it distorts the CKP signal, causing DTC P0389, in spite of there being no actual problem with the CKP sensor or wiring.
- Cars in Storage – Unfortunately, while looking for nesting materials and cleaning house, these little critters might find your wiring offensive or even tasty, resulting in open circuit problems.
- Older Cars – Over time, plastic and rubber tends to become brittle and less flexible, which can lead to connector breakage and wire insulation damage. In turn, this may cause corrosion, open circuits, or short circuits.
What are the symptoms of code P0389 ?
If the ECU only sometimes detects a CKP signal, it will set a diagnostic trouble code (DTC), DTC P0389 – Crankshaft Position B Sensor Circuit Intermittent, and illuminate the MIL or CEL (malfunction indicator lamp or check engine light). Sensor B is indicative of the secondary CKP in a system that may utilize multiple crankshaft position sensors for various functions. If the signal is weak (poor installation or faulty sensor) or there is a wiring problem (loose connector or wire harness damage), this could result in an intermittent CKP signal. Without a CKP signal, you may experience no-start or start-stall conditions.
Depending on year, make, and model, the ECU may be able to use the CMP (camshaft position sensor) to estimate engine speed and position, so the engine will run, but not at its most-efficient. In this case, you may experience hard starting, rough idle, or poor acceleration.
How do you troubleshoot code P0389 ?
Since P0389 refers to a circuit problem, we can focus our attention on electrical problems, but we still cannot rule out the sensor or reluctor ring. Fortunately, because the CKP sensor and signal is very similar to the CMP sensor and signal, we can follow the same troubleshooting steps to determine why DTC P0389 is stored in ECU memory.
- Visual Inspection – Make sure all connectors are properly connected. Check the wiring harness for damage.
- Sensor Inspection – Check for resistance, an open circuit or short circuit is a definite fault, but check the repair manual for an exact resistance range. You can check for signal by setting your DVOM (digital volt-ohm meter) to AC mV, and cranking the engine.
- Harness Inspection – Check for open circuits and short circuits in the harness between the ECU and CKP sensor.
Codes Related to P0389
If the engine doesn’t run, additional DTCs may be stored in ECU memory, such as:
- P0385 – Crankshaft Position Sensor B Circuit Malfunction
- P0386 – Crankshaft Position Sensor B Circuit Range/Performance
- P0387 – Crankshaft Position Sensor B Circuit Low Input
- P0388 – Crankshaft Position Sensor B Circuit High Input
- P0389 – Crankshaft Position Sensor B Circuit Intermittent
- P0340 – Camshaft Position Sensor Circuit Malfunction (Bank 1)
- P0341 – Camshaft Position Sensor Circuit Range/Performance (Bank 1)
- P0342 – Camshaft Position Sensor Circuit Low Input (Bank 1)
- P0343 – Camshaft Position Sensor Circuit High Input (Bank 1)
- P0344 – Camshaft Position Sensor Circuit Intermittent (Bank 1)
- P0345 – Camshaft Position Sensor Circuit (Bank 2)
- P0346 – Camshaft Position Sensor Circuit Range/Performance (Bank 2)
- P0347 – Camshaft Position Sensor Circuit Low Input (Bank 2)
- P0348 – Camshaft Position Sensor Circuit High Input (Bank 2)
- P0349 – Camshaft Position Sensor Circuit Intermittent (Bank 2)
- P0725 – Engine Speed Sensor Circuit
If the engine does run, these additional DTCs may be stored in ECU memory:
- P0300 – Random/multiple cylinders – Misfire Detected
- P030x – Cylinder X – Misfire Detected
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