Site icon My Pro Street

P0385 Code: Crankshaft Position Sensor “B” Circuit Malfunction

The P0385 code identifies an electrical malfunction in the Crankshaft Position Sensor B circuit. Diagnose its signal, wiring, reluctor and PCM input.

The P0385 OBD-II trouble code means the powertrain control module has detected an electrical malfunction in the Crankshaft Position Sensor “B” circuit.

This code applies to vehicles equipped with a secondary crankshaft-position sensor or a separately identified CKP Sensor B circuit. It does not automatically mean the sensor itself has failed. Damaged wiring, missing reference voltage, a poor ground, connector corrosion, a damaged reluctor wheel or an internal PCM problem can produce the same code.

Most importantly, Sensor B does not automatically mean Bank 2. It identifies the second crankshaft-position input defined by the manufacturer. Check the vehicle’s service information before replacing whichever sensor happens to be hardest to reach. Automotive engineering already provides enough surprises without volunteering for extra ones.

P0385 Quick Reference

ItemDetails
Trouble codeP0385
Code definitionCrankshaft Position Sensor “B” Circuit Malfunction
System affectedEngine-position and ignition-timing control
Fault typeElectrical malfunction or missing/invalid CKP Sensor B signal
Common causesFailed sensor, damaged wiring, poor connection, missing power or ground, damaged reluctor wheel
Common symptomsCheck Engine Light, stalling, hard starting, no-start condition, rough running or reduced power
Typical severityModerate to severe
Safe to drive?Not recommended until the cause is identified
Repair difficultyIntermediate to advanced

What Does the P0385 Code Mean?

P0385 indicates that the PCM cannot detect a valid electrical signal from Crankshaft Position Sensor B or has detected a general malfunction in that sensor’s circuit.

The crankshaft-position signal allows the PCM to determine:

On an engine using two crankshaft-position inputs, the PCM may compare Sensor A and Sensor B for accuracy and redundancy. If the Sensor B circuit loses power, loses ground, becomes open or shorted, or produces an invalid waveform, the PCM may store P0385.

Because P0385 is a general circuit-malfunction code, it does not specify whether the signal is too low, too high or intermittent. Those more specific conditions are covered by later codes in the same family:

Use the complete P-code OBD-II guide to identify other related powertrain faults.

What Is Crankshaft Position Sensor B?

Crankshaft Position Sensor B is the secondary crankshaft-position input on vehicles designed with more than one CKP sensor or signal circuit.

Its location and function vary by manufacturer. The sensor may be installed near:

Some engines use two physical crankshaft sensors. Others may use multiple crankshaft signals for redundancy, engine-position resolution or synchronization.

Sensor B does not universally identify the rear sensor, the passenger-side sensor or Bank 2. Crankshaft sensors normally monitor the crankshaft itself, which is shared by both cylinder banks. The letter designation must be confirmed using the manufacturer’s component-location information.

How a Crankshaft-Position Sensor Works

A crankshaft-position sensor monitors a toothed or slotted trigger wheel attached to the crankshaft, flywheel or flexplate. As the wheel rotates, the sensor creates an electrical signal containing a series of pulses.

The PCM counts those pulses and uses a missing tooth, wide gap or other reference feature to determine the crankshaft’s exact position.

Two common sensor designs are used.

Magnetic or Variable-Reluctance Sensor

A magnetic CKP sensor commonly uses two wires and generates its own alternating-current signal as the reluctor teeth pass the sensor tip.

Its output voltage generally increases with crankshaft speed. During slow cranking, a weak sensor, excessive air gap or damaged reluctor can produce insufficient voltage.

Hall-Effect Sensor

A Hall-effect sensor normally uses three circuits:

The sensor switches the signal between high and low voltage as the trigger wheel rotates. A Hall-effect sensor requires proper power and ground before it can produce a valid signal.

Knowing which sensor design is installed is essential. A resistance test that may provide useful information on a magnetic pickup is usually inappropriate for an active Hall-effect sensor.

Symptoms of a P0385 Code

P0385 symptoms depend on how heavily the PCM relies on Sensor B and whether another crankshaft-position input remains operational.

Possible symptoms include:

Some vehicles can continue operating using CKP Sensor A or a calculated substitute value. Others may lose ignition or injector control entirely when Sensor B fails.

If the starter turns the engine but combustion never begins, follow the broader engine cranks but won’t start guide to verify spark, injector command, fuel pressure and engine-position data.

If the engine shuts off only after reaching operating temperature, the engine stalls when warm diagnostic guide can help separate a heat-sensitive crank sensor from fuel, ignition and charging-system problems.

Common Causes of P0385

Potential causes include:

  1. Failed Crankshaft Position Sensor BInternal sensor electronics, windings or magnets can fail from heat, vibration and age.
  2. Open Sensor Signal WireA broken wire can prevent the Sensor B signal from reaching the PCM.
  3. Signal Circuit Shorted to GroundDamaged insulation may allow the signal wire to contact the engine block, chassis or another ground circuit.
  4. Signal Circuit Shorted to VoltageContact with a reference-voltage or battery-voltage circuit can hold the signal outside its operating range.
  5. Missing Sensor Reference VoltageA Hall-effect sensor cannot operate without its specified supply voltage.
  6. Poor Sensor GroundCorrosion, loose terminals or high resistance in the ground circuit can distort or eliminate the sensor signal.
  7. Loose or Damaged ConnectorOil, water, road debris or improper previous repairs can damage the sensor connector.
  8. Incorrect Sensor Air GapExcessive clearance between the sensor and reluctor wheel can weaken the signal.
  9. Damaged Reluctor WheelCracked, bent, missing or contaminated teeth can prevent a valid waveform.
  10. Excessive Crankshaft End Play

Movement of the crankshaft can change the sensor air gap and destabilize the signal.

  1. Improper Sensor Installation

Debris under the mounting surface, an incorrect spacer or a sensor that is not fully seated can alter the air gap.

  1. Incorrect Replacement Sensor

Some aftermarket sensors have the wrong electrical characteristics or poor waveform quality.

  1. PCM Connector or Driver Fault

Terminal damage or an internal PCM input-circuit failure can trigger P0385, although this is less common.

  1. Timing or Mechanical Damage

A shifted reluctor, damaged flexplate or improperly installed timing component may disrupt the expected signal.

How Serious Is the P0385 Code?

P0385 should be treated as a moderate-to-severe fault.

The crankshaft-position signal is one of the PCM’s most important engine inputs. If Sensor B fails completely, the engine may stall without warning or refuse to restart. A vehicle that currently runs normally may become unreliable as heat, vibration or moisture worsens the electrical fault.

Continued driving is not recommended when P0385 is accompanied by:

A sudden engine stall can also reduce power-steering and brake-assist performance, making an electrical sensor problem considerably less entertaining once traffic becomes involved.

P0385 vs. P0335

P0385 and P0335 describe similar electrical faults but apply to different crankshaft-position inputs.

CodeDefinitionCircuit covered
P0335Crankshaft Position Sensor “A” Circuit MalfunctionPrimary or designated Sensor A circuit
P0385Crankshaft Position Sensor “B” Circuit MalfunctionSecondary or designated Sensor B circuit

Do not assume the two sensors are interchangeable. They may use different mounting locations, connector shapes, signal patterns or part numbers.

The safest approach is to identify Sensor B through the wiring diagram and factory component-location information before disconnecting anything.

P0385 vs. P0386, P0387, P0388 and P0389

The P0385 family separates a general circuit failure from specific electrical conditions.

CodeMeaningDiagnostic focus
P0385Sensor B circuit malfunctionGeneral circuit or missing-signal failure
P0386Sensor B range/performanceSignal exists but is implausible or outside the expected performance range
P0387Sensor B circuit lowSignal voltage remains below the expected range
P0388Sensor B circuit highSignal voltage remains above the expected range
P0389Sensor B circuit intermittentSignal drops out or becomes unstable intermittently

If one of the more specific codes is stored with P0385, begin with the specific voltage or performance condition.

How to Diagnose the P0385 Code

Proper diagnosis requires a scan tool, wiring diagram and digital multimeter. An oscilloscope is strongly recommended because a crankshaft sensor is a signal-producing component, and a waveform tells far more than a sensor’s resistance measurement.

1. Confirm the Stored Code

Connect an OBD-II scan tool and record:

Do not immediately erase the codes. Freeze-frame data may reveal whether the failure occurred during cranking, at idle, while hot or at a particular engine speed.

2. Check for Related Codes

Look for codes involving:

Multiple sensors losing their shared reference voltage or ground suggest a circuit problem rather than several sensors failing simultaneously. Sensors rarely organize group resignations.

3. Verify the Complaint

Attempt to start and run the engine while monitoring scan-tool RPM.

During cranking, most scan tools should display a plausible engine-speed value. A reading of zero RPM suggests the PCM is not receiving a usable crankshaft-position signal, although some vehicles may display RPM from Sensor A while Sensor B remains faulty.

Watch for:

4. Identify Sensor B Correctly

Use factory service information to identify:

Do not identify Sensor B solely by physical location. The manufacturer’s designation controls the diagnosis.

5. Inspect the Sensor and Wiring

Switch the ignition off and inspect the entire accessible circuit.

Look for:

Inspect the harness where it passes behind the engine and near the bellhousing. These areas experience heat, vibration and limited visibility—a lovely combination when you enjoy electrical diagnosis upside down.

6. Check Battery Voltage

Cranking voltage that drops excessively can reduce sensor output and disrupt PCM operation.

Test:

Repair a weak battery, poor cable connection or charging-system fault before condemning the sensor.

7. Test Hall-Effect Sensor Power and Ground

If Sensor B is a Hall-effect design, disconnect the sensor and switch the ignition on.

Using a high-impedance digital multimeter, verify:

Do not assume every Hall sensor uses five volts. Some operate on a different regulated supply or battery voltage.

Test the ground with a voltage-drop method whenever possible. A continuity beep can pass through resistance that becomes unacceptable under operating conditions.

8. Test a Magnetic Sensor Circuit

If Sensor B is a two-wire magnetic pickup, inspect its resistance only when the manufacturer provides a specification.

Then measure alternating-current voltage while cranking. A sensor that produces little or no AC voltage may have:

Resistance alone cannot confirm waveform quality. A sensor can pass an ohmmeter test and still fail when hot or under operating speed.

9. Inspect the Signal With an Oscilloscope

Back-probe the signal using the manufacturer-approved procedure.

A healthy Hall-effect sensor should produce a clean digital waveform that switches consistently between its specified high and low states.

A healthy magnetic sensor should produce an alternating waveform with consistent amplitude and spacing.

Look for:

If the vehicle provides both Sensor A and Sensor B signals, compare them simultaneously. The relationship between the two waveforms may reveal a shifted reluctor, incorrect sensor, wiring fault or mechanical timing problem.

10. Compare the Signal at the Sensor and PCM

If Sensor B produces a proper waveform at its connector, test the same signal at the PCM.

A good signal at the sensor but a missing or distorted signal at the PCM points toward:

If the waveform reaches the PCM correctly but P0385 remains, verify PCM powers, grounds, connector condition and software before considering module replacement.

11. Test Circuit Continuity

Disconnect both the sensor and PCM before performing resistance checks.

Test the Sensor B circuits for:

Never use an ohmmeter on a powered circuit.

When testing terminal fit, use the correct terminal-drag tool. Forcing an oversized probe into the connector can spread the terminal and create a new intermittent fault, because apparently one electrical problem was not enough.

12. Inspect the Reluctor Wheel and Air Gap

If the electrical circuit tests correctly, inspect the mechanical trigger.

Possible problems include:

Some reluctor wheels are located inside the engine or transmission and cannot be inspected directly without significant disassembly. In those cases, waveform analysis becomes especially valuable.

13. Test for Heat-Related Failure

If the engine stalls when warm but restarts after cooling, monitor the Sensor B waveform as temperature rises.

You can also carefully heat the sensor and harness using an approved method while watching the signal. Avoid open flames and uncontrolled heat. The objective is diagnosis, not converting the wiring harness into performance art.

A waveform that disappears consistently at a certain temperature strongly suggests an internal sensor or connection failure.

14. Consider the PCM Last

PCM failure is possible but uncommon.

Before replacement, confirm:

PCM replacement may require programming, security-system initialization and crankshaft-position relearn procedures.

Common P0385 Diagnostic Mistakes

Avoid these common mistakes:

Repairs That May Fix P0385

The proper repair depends on the diagnostic results.

Possible repairs include:

When replacing the sensor, compare the new and original components carefully. Sensor length, mounting depth and electrical design must match.

Estimated P0385 Repair Costs

Actual costs vary by vehicle and sensor accessibility.

RepairEstimated cost
Diagnostic inspection$100–$220
Connector or minor wiring repair$100–$350
Crankshaft Position Sensor B replacement$180–$650
Major harness repair$300–$1,000
Reluctor-wheel or flexplate replacement$700–$2,500
PCM software update$100–$300
PCM replacement and programming$800–$2,500

A sensor mounted externally near the crankshaft pulley may be relatively inexpensive to replace. A sensor buried behind the transmission, starter or other components will cost more because accessibility remains undefeated as the automotive industry’s favorite labor multiplier.

Can You Drive With a P0385 Code?

Driving with P0385 is not recommended until the cause is identified.

The vehicle may continue running if the PCM can rely on another position signal, but it may also:

Stop driving and arrange diagnosis if the engine stalls, loses power, cranks without starting or displays additional timing-related codes.

For general warning-light information, review what the Check Engine Light means.

How to Verify the Repair

After completing the repair:

  1. Reconnect all sensors and modules.
  2. Confirm that the harness is secured away from heat and moving parts.
  3. Clear current and pending codes.
  4. Start the engine while monitoring RPM and synchronization data.
  5. Verify a stable Sensor B waveform.
  6. Allow the engine to reach operating temperature.
  7. Perform a harness wiggle test where appropriate.
  8. Complete a manufacturer-specified drive cycle.
  9. Recheck for current and pending codes.
  10. Perform a crankshaft-position relearn if required.

The repair is confirmed only when the signal remains stable and P0385 does not return under the conditions that originally triggered it.

Frequently Asked Questions

What does the P0385 code mean?

P0385 means the PCM detected a general electrical malfunction in the Crankshaft Position Sensor B circuit.

Does P0385 mean the crankshaft sensor is bad?

Not necessarily. The sensor may have failed, but damaged wiring, poor power or ground, connector corrosion, incorrect air gap, reluctor damage or PCM problems can produce the same code.

Is Crankshaft Position Sensor B located on Bank 2?

Not necessarily. Sensor B identifies the manufacturer-designated secondary crankshaft-position input. It does not universally mean Bank 2.

What is the difference between P0335 and P0385?

P0335 applies to the Crankshaft Position Sensor A circuit. P0385 applies to the Crankshaft Position Sensor B circuit.

Can P0385 cause a no-start condition?

Yes. If the PCM requires Sensor B to calculate engine position, losing its signal can prevent spark, injector operation or engine synchronization.

Can P0385 cause the engine to stall?

Yes. A Sensor B signal that fails while the engine is running may cause intermittent stalling or reduced-power operation.

Can a damaged reluctor wheel cause P0385?

Yes. A cracked, loose or damaged reluctor wheel can prevent the sensor from generating a valid signal even when the electrical circuit is intact.

How do you test Crankshaft Position Sensor B?

Identify the sensor type, verify its power and ground, inspect the wiring and measure its waveform with an oscilloscope. Compare the signal at the sensor and PCM.

Does replacing Sensor B require a relearn?

Some vehicles require a crankshaft-position variation relearn after sensor replacement or related repairs. Follow the manufacturer’s service procedure.

How much does it cost to repair P0385?

Minor wiring repairs may cost approximately $100 to $350. Sensor replacement commonly ranges from $180 to $650, while internal reluctor or PCM repairs can exceed $1,000.

Final Thoughts

P0385 identifies a malfunction in the Crankshaft Position Sensor B circuit. The sensor is a common suspect, but it is only one part of the circuit.

Start by identifying Sensor B correctly. Then check battery voltage, connector condition, sensor power, ground and signal integrity. An oscilloscope comparison between Sensor A and Sensor B provides the clearest evidence when the vehicle uses two crankshaft-position inputs.

Replacing a sensor because its name appears in the code definition may occasionally work. Testing the circuit first works considerably more often—and leaves fewer perfectly good sensors sitting in the box marked “apparently not that.”

Visit the OBD-II Doctor for more code-specific diagnostic guides or use the complete P-series OBD-II code list to identify additional powertrain faults.

Exit mobile version