P078E — Shift Timing Solenoid B Intermittent

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P078E is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the shift timing solenoid b intermittent for damage, corrosion, chafing or poor contact.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P078E does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P078E (parts and labor, USD, independent shop rates): Repair wiring or connectors: $80–$250; Replace the faulty sensor or actuator: $150–$500; Control module repair: $300–$1,000. Overall, fixing P078E usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How do I diagnose P078E myself?

Start with a scan: confirm P078E, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the sensor and actuator circuits, and verify the suspect component against live data before buying parts.

What is the most common cause of P078E?

The most common causes are: poor ground connection, control module driver fault, faulty sensor or actuator of the affected circuit.

Will P078E clear itself?

Sometimes P078E clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How much does it cost to fix P078E?

Repair wiring or connectors — $80–$250; Replace the faulty sensor or actuator — $150–$500; Control module repair — $300–$1,000. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What does OBD2 code P078E mean?

Shift Timing Solenoid B Intermittent (P078E): a powertrain (engine/transmission) fault affecting the sensor and actuator circuits. The car is usually drivable while you plan the repair. Most often caused by poor ground connection, control module driver fault, faulty sensor or actuator of the affected circuit.

When your OBD2 scanner pulls code P078E, it's telling you that the transmission control module has detected an abnormality in one of the solenoid circuits responsible for shift timing. Specifically, P078E refers to "Shift Timing Solenoid B Intermittent" — a fault where the signal from this actuator flickers in and out rather than holding steady. The transmission control unit (TCU) or engine control unit (ECU) constantly watches this circuit, and the moment the signal behaves erratically for long enough, it logs P078E and triggers the Check Engine light.

Solenoid B is one of several electrohydraulic valves inside the automatic transmission that direct fluid pressure to engage the correct gear. When the TCU commands a shift, it energizes the appropriate solenoid to route fluid, and the transmission clutches respond accordingly. If the signal to that solenoid is intermittent — sometimes present, sometimes not — the clutch applies unevenly or at the wrong time, which degrades shift quality and can push the transmission into a protective limp mode. The ECU stores freeze frame data alongside P078E, capturing engine speed, load, coolant temperature, and vehicle speed the instant the fault occurred. That snapshot is the most useful starting point for figuring out what actually went wrong.

The key thing to understand about P078E is that "intermittent" in the code name doesn't mean harmless — it means inconsistent. An intermittent fault can be far more frustrating to diagnose than a hard failure because the problem may not show up during a quick test drive.

Symptoms of P078E

P078E affects transmission behavior rather than engine output, so you'll notice drivability changes rather than under-hood symptoms. The most common complaints include the following:

The Check Engine light stays illuminated after the fault is detected.
The transmission may shift roughly, hesitate between gears, or refuse to shift into higher gears.
The vehicle could enter limp mode, restricting operation to second or third gear only.
Fuel economy may drop noticeably because the transmission isn't shifting optimally.
In some cases, the affected solenoid circuit stops working entirely until the issue is resolved.
Symptoms may come and go, which is typical of an intermittent electrical problem rather than a mechanical one.

Common causes

P078E is an electrical fault code at its core. The most likely culprits are wiring and connector problems, which are far more common in high-mileage vehicles than actual solenoid failure. The following issues can trigger this code:

Broken, frayed, or chafed wiring in the harness leading to Shift Timing Solenoid B.
Corrosion or moisture intrusion at the solenoid connector, creating high resistance.
A loose or partially backed-out connector that makes intermittent contact.
An open circuit or a short to ground or power caused by damaged insulation.
A blown fuse that supplies voltage to the solenoid circuit.
A faulty shift timing solenoid itself — less common, but possible with age or fluid contamination.
Poor ground connection at the transmission case affecting the solenoid return path.

How to diagnose P078E

Diagnosing an intermittent electrical fault requires a methodical approach. Rushing to replace the solenoid often wastes money because the wiring is usually the real culprit. Follow these steps to narrow down the cause:

Connect an OBD2 scanner, retrieve all stored codes including P078E, and save the freeze frame data. Record the exact conditions — rpm, load, temperature, and speed — captured when the fault first appeared. This tells you whether the problem occurs during cold starts, heavy acceleration, or specific gear changes.
Check for any other diagnostic trouble codes alongside P078E. Related codes in the transmission range (P0700–P0799) often point to a shared root cause, such as low fluid or a faulty sensor feeding bad data to the TCU.
Perform a thorough visual inspection of the wiring harness and connector at Shift Timing Solenoid B. Look for cracked insulation, broken strands inside the wire, greenish corrosion on the pins, and any signs of the connector not being fully seated.
With the connector unplugged, use a multimeter to check reference voltage at the power side and verify ground continuity on the return side. Compare your readings to the specifications in the repair manual for your vehicle.
Run a wiggle test on the harness while monitoring live data on the scanner. Any signal dropout or fluctuation while flexing the wires confirms an intermittent open or poor connection.
After addressing any wiring issues found, clear P078E, complete a full drive cycle that reproduces the conditions from the freeze frame, and verify the code does not return.

Repair options and costs

Labor rates vary by location, but the figures below reflect typical independent shop pricing in USD. Always address the least expensive potential causes before moving to component replacement.

Wiring repair or connector replacement: $80–$250. Often involves rerouting a section of harness, cleaning pins, or splicing in a new connector. This resolves the majority of P078E cases.
Shift Timing Solenoid B replacement: $150–$500. The solenoid itself is relatively inexpensive, but labor varies significantly depending on whether the transmission pan must be dropped. Some solenoids are accessible through the transmission oil pan.
Control module diagnosis or repair: $300–$1,000. In rare cases, the TCU itself has an internal fault. Reprogramming or replacing the module is the last resort after all wiring and solenoid tests pass.

Total out-of-pocket for P078E typically falls between $80 and $1,000 depending on what is actually wrong. A precise electrical diagnosis before purchasing parts is strongly recommended — the cheapest fix solves the problem far more often than the most expensive one.

Can you drive with P078E?

In most vehicles, P078E does not immobilize the car outright. You can typically continue driving, though you may experience harsh shifting, reduced fuel economy, or limited gear selection while the transmission operates in its fail-safe mode. Treat the warning more urgently if you notice stalling, complete loss of shift response, or any brake and steering warnings on the dash — these indicate a broader system problem that warrants immediate attention. Otherwise, schedule a diagnostic appointment within a week or two to prevent the intermittent fault from causing additional transmission wear.