P0378 — Timing Reference High Resolution Signal B Intermittent/Erratic Pulses

P0378 — Timing Reference High Resolution Signal B Intermittent/Erratic Pulses. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, corroded, loose or damaged connector, open or shorted wiring in the circuit.

powertrain (engine/transmission)

Is it safe to drive?

Caution: drive only if the engine remains stable P0378 indicates an intermittent high-resolution timing reference, so the engine may stall or lose power without warning. A short, low-load drive may be reasonable if it runs smoothly, but stop driving if it stumbles, stalls, flashes the check-engine light, or enters reduced-power mode.

Typical symptoms

  • Check engine light illuminated with P0378 stored or listed as a pending code.
  • Intermittent rough idle, hesitation, or a noticeable stumble.
  • Brief surging or loss of power while the Timing Reference Signal B is dropping out.
  • Unexpected engine stall or difficulty restarting after the fault disappears.
  • Reduced-power or fail-safe engine operation on some vehicles.
  • P0378 may remain stored without current symptoms because the signal fault is intermittent.

Common causes

  • Internal intermittent failure of the sensor producing Timing Reference High Resolution Signal B, commonly designated the camshaft position sensor B.
  • Open, short, chafed wiring, or a loose or corroded connector terminal in the Signal B circuit.
  • Incorrect sensor mounting or excessive sensor-to-reluctor air gap that distorts the reference pulse pattern.
  • Oil contamination, metal debris, damaged teeth, or a cracked reluctor causing missing or erratic Signal B pulses.
  • Poor sensor grounding, unstable supply voltage, or electrical noise affecting the Signal B output.
  • An incompatible replacement sensor or damaged cam-sprocket or reluctor mount producing an unstable reference pattern.

How to diagnose with an OBD scanner

  1. Confirm P0378 and correlate the event Connect an OBD2 scanner, such as an ELM327 adapter with AIScanAuto, and verify that P0378 is stored or pending. Save freeze-frame data and, if supported, monitor crank and cam synchronization, RPM, and load while reproducing the fault.
  2. Inspect the Signal B wiring and connector With the ignition off, inspect the Timing Reference Signal B connector for backed-out pins, corrosion, oil, water, and broken locking tabs. Follow the harness for chafing, pinching, or damage near heat sources and moving components.
  3. Check the sensor electrically and on a scope Verify supply voltage, ground integrity, and the sensor output against the vehicle wiring diagram. A digital oscilloscope should show a stable pulse train; missing pulses during light harness movement point to wiring, while a clean but irregular output suggests the sensor or reluctor.
  4. Examine the reluctor and timing relationship Inspect the Signal B reluctor for debris, damaged teeth, cracking, or a loose hub. Check cam-to-crank synchronization and chain condition. A skipped chain tooth more commonly causes a correlation code, so confirm mechanical timing before ordering timing components.
  5. Repair and validate P0378 Repair the wiring or connector, reseat the sensor at the specified air gap, or replace the Signal B sensor and damaged reluctor as required. Clear P0378, confirm live data remains synchronized, and road test under several loads to verify the intermittent fault is gone.

Approximate repair cost

A typical independent-shop range is USD 150-500 for diagnosis and repair involving the Timing Reference Signal B sensor, connector, or wiring. Reluctor or timing-chain work may raise the total to roughly USD 800-1,500. These figures are estimates and vary by region and vehicle.

Common questions

What exactly does P0378 report?

P0378 means the ECU received intermittent or erratic pulses from the high-resolution Timing Reference Signal B circuit, commonly the cam-position reference used for fuel-timing control.

Does P0378 always mean the camshaft position sensor is bad?

No. P0378 identifies an unstable Signal B reference, so the sensor, wiring, connector, reluctor, mounting, or power and ground circuits must be tested before replacing the sensor.

Can I drive a vehicle with P0378?

Only cautiously if the engine runs normally and P0378 does not return. Avoid sustained driving if there is stalling, misfire, hesitation, warning-light flashing, or reduced power.

Why should the wiring be checked before replacing the sensor for P0378?

A chafed wire or poor terminal can mimic a failed high-resolution sensor and produce the same intermittent pulse loss recorded as P0378.

When P0378 shows up on a scan tool, the engine control unit has identified a fault with the high-resolution timing reference signal on circuit B. This is not a simple sensor reading problem — it means the precise pulse train the ECU uses to calculate crankshaft position and timing is either missing, noisy, or erratic. The OBD2 system classifies this as a powertrain fault because it interferes with the precise fuel delivery and ignition timing the engine needs to run correctly.

Modern engines rely on high-frequency signals from the crankshaft position sensor or a dedicated reluctor wheel to track the exact rotational position of the engine. The control module compares this primary signal against secondary reference points to make sure the timing data is accurate. When those high-resolution pulses deviate from expected values — either dropping out intermittently or showing incorrect spacing — the ECU logs P0378. It typically takes multiple failed checks across more than one drive cycle before the code is fully stored, along with a freeze frame snapshot capturing engine speed, load, coolant temperature, and vehicle speed at the moment the fault occurred.

Reading that freeze frame before anything else saves time. It tells you exactly what conditions triggered the code, so you can reproduce them during testing rather than guessing.

Symptoms of P0378

  • Check Engine Light is illuminated and stays on
  • The system that triggered the code may operate intermittently or stop working entirely
  • Reduced engine performance or rough operation in some vehicles
  • Possible limp-home mode activation depending on which circuit is affected
  • Increased fuel consumption reported by some drivers
  • In rare cases, stalling or no-start conditions if the timing signal is completely lost

Common Causes of P0378

Damaged or failing wiring and connectors are the most frequent source of this code. Corrosion at the connector pins, broken wires inside the harness, or loose grounds all create the exact kind of intermittent signal dropout the ECU is watching for.

Blown fuses or an interrupted power supply to the timing reference circuit can also set P0378. Replacing the fuse clears the code only if the underlying short or overload has been fixed.

A faulty crankshaft position sensor, camshaft position sensor, or related actuator on circuit B can fail internally, sending corrupted pulses to the control module.

Control module internal driver failures are less common but possible, especially on higher-mileage vehicles where the PCM has been subjected to heat and voltage stress.

How to Diagnose P0378

  1. Connect an OBD2 scanner and confirm P0378 is stored. Save the freeze frame data immediately — that snapshot of engine conditions when the fault was detected is your roadmap for reproducing the problem.
  2. Look at all other stored codes. Related P03xx misfire codes or other sensor faults often point to the root cause. Check manufacturer TSB databases for your specific make and model — some P0378 failures have documented factory fixes or software updates available.
  3. Perform a thorough visual inspection of the wiring harness and connectors tied to the timing reference circuit B. Look for chafed insulation, bent or corroded pins, moisture intrusion, and any signs of previous repairs that may have been done incorrectly.
  4. With the connector unplugged, check for proper reference voltage, ground continuity, and signal wire integrity at the component. Compare your readings to manufacturer specifications.
  5. Reconnect the sensor and run a live data test while gently wiggling the harness. Any signal dropout or fluctuation indicates a broken wire or loose connection inside the insulation.
  6. Clear the code and complete a drive cycle that includes the conditions from the freeze frame data. If P0378 does not return, the fault was likely intermittent and may not have been fully resolved — monitor closely.

Repair Options for P0378

If the wiring inspection reveals damage, repairing the harness or connectors typically runs between $80 and $250 for parts and labor at an independent shop.

Replacing a faulty crankshaft or camshaft position sensor on circuit B generally costs $150 to $500 depending on vehicle make and local labor rates.

Control module diagnosis and repair or replacement is the most expensive route at $300 to $1,000, and should only be pursued after the wiring and sensors have been ruled out.

How Much Does Fixing P0378 Cost?

The total depends entirely on which component caused the fault. Wiring and connector repairs fall in the $80–$250 range, sensor replacement in the $150–$500 range, and PCM work in the $300–$1,000 range. Most shop labor rates run $75–$125 per hour, so the total bill varies with how long the diagnosis takes. The most practical approach is to rule out cheap fixes first — wiring issues and blown fuses are far more common than control module failure.

Can You Drive with P0378?

In most cases the vehicle remains drivable. You may notice slightly reduced performance or one auxiliary system not functioning, but the engine will typically still run. Treat the code as urgent if you experience stalling, no-start conditions, or any warning lights related to brakes or steering assistance. Otherwise, schedule diagnosis within a week or two to prevent the issue from worsening.

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