P0855 — Drive Switch Input Circuit High

P0855 — Drive Switch Input Circuit High. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: open or shorted wiring in the circuit, faulty sensor or actuator of the affected circuit, poor ground connection.

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 P0855 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 drive switch input for damage, corrosion, chafing or poor contact.
Subsystem check With the drive switch input disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
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 P0855 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0855 (parts and labor, USD, independent shop rates): Replace the faulty sensor or actuator: $150–$500; Repair wiring or connectors: $80–$250; Control module repair: $300–$1,000. Overall, fixing P0855 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

What are the symptoms of P0855?

Drivers most often notice: possible limp mode depending on the affected component, the affected system operates intermittently or not at all, Check Engine Light on, increased fuel consumption in some cases.

What is the most common cause of P0855?

The most common causes are: open or shorted wiring in the circuit, faulty sensor or actuator of the affected circuit, poor ground connection.

How much does it cost to fix P0855?

Replace the faulty sensor or actuator — $150–$500; Repair wiring or connectors — $80–$250; 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.

Will P0855 clear itself?

Sometimes P0855 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.

Is it safe to drive with P0855?

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.

When your scan tool pulls code P0855, the powertrain control module is telling you it has detected a problem with the drive switch input circuit — specifically, the voltage on that circuit is sitting higher than it should. "Circuit high" is the technical way of saying the signal line is showing close to full battery voltage when it should be at a lower, controlled level. That elevated voltage triggers the module to flag the fault and light up the Check Engine lamp. The control unit continuously monitors this circuit while the engine is running, and if the voltage stays out of the expected window long enough across multiple drive cycles, P0855 gets stored permanently in memory.

What causes that voltage to climb in the first place? There are a few distinct possibilities. The signal wire may have shorted directly to a power source, forcing the circuit high. Alternatively, the ground return path for the drive switch may have broken or lost continuity, which can also make the module read a phantom high condition. A failed component that internally pulls the signal to battery voltage will do the same thing. Each of these scenarios produces the same scan tool result, which is why a methodical approach to diagnosis matters. When the code sets, the module also saves freeze frame data — a snapshot of engine rpm, load, temperature, and vehicle speed at the exact moment the fault was detected. That snapshot is your best starting point, because it tells you under what conditions the problem actually occurs.

Symptoms of P0855

P0855 rarely hides. The Check Engine Light almost always comes on when the fault code is active. Beyond that warning lamp, you may notice one or more of the following depending on which specific circuit or component the drive switch controls:

The vehicle enters limp mode, limiting power or disabling certain functions to protect the drivetrain.
The system tied to the drive switch — such as a transfer case, shift inhibit, or clutch position circuit — operates intermittently or stops working altogether.
Fuel economy worsens as the engine management system compensates for the abnormal signal.
In rare cases, no obvious driveability symptoms are present besides the illuminated dash light, which makes the code easy to ignore — don't.

What causes P0855?

The root cause usually falls into one of three categories: wiring problems, a failed component, or a control module fault. Here is the breakdown in order of how often each tends to show up:

The drive switch input sensor or associated actuator has failed and is pulling the signal line high.
The signal wire is shorted to battery positive somewhere along the harness.
The ground return circuit for the drive switch input is open or has high resistance.
The ground connection at the component or control module is loose, corroded, or damaged.
The control module driver that manages the circuit has itself failed.
A corroded, loose, or physically damaged connector is interrupting the signal path.
A fuse that feeds power to the circuit has blown, which can sometimes produce a related high-voltage condition depending on circuit design.

How to diagnose P0855

Diagnosis follows a logical elimination process. Work from the outside of the circuit inward, and always start with the freeze frame data.

Connect an OBD2 scanner and confirm P0855 is stored. Record the freeze frame data before clearing anything — that snapshot tells you engine load, rpm, temperature, and speed when the fault triggered, which guides the rest of your investigation.
Pull all stored codes from the module. Related codes often point directly to the failing part. After that, check for any factory Technical Service Bulletins (TSBs) for your specific make and model — some P0xxx codes have known factory fixes or software updates that a parts swap will never solve.
Perform a thorough visual inspection of the wiring harness and connectors associated with the drive switch input. Look for chafed wire insulation, green corrosion buildup, bent pins, or any sign of moisture intrusion.
With the drive switch input connector disconnected, probe the harness side and measure signal voltage. If the reading is still high with the component unplugged, the problem is in the wiring — specifically a short to power. If the voltage drops to normal reference range, the failed component is the culprit.
At the component connector itself, verify that reference voltage, ground, and signal continuity are all within specification using a multimeter. A missing ground or incorrect reference voltage explains many intermittent faults.
Perform a wiggle test on the harness while monitoring live data on the scanner. Any signal dropout or fluctuation points to a broken wire that only shows under movement.
Clear the code, run the vehicle through a complete drive cycle that recreates the conditions from the freeze frame data, and verify that P0855 does not return. If it resets, the root cause has not been addressed.

Repair options and cost

Before replacing expensive components, rule out the simple stuff first. Wiring repairs and connector cleaning or replacement are far cheaper than swapping a control module. Typical repair costs for P0855, using independent shop labor rates in USD:

Replace faulty sensor or actuator — $150 to $500
Repair wiring or connectors — $80 to $250
Control module repair or replacement — $300 to $1,000

How much does fixing P0855 cost?

The total bill hinges entirely on what is actually broken. Most of the time, the fault is a failed sensor, actuator, or a simple wiring issue, and those repairs fall on the lower end of the scale. Control module replacement is the outlier — it is the most expensive scenario but also the least likely, so it should be your last resort after you have confirmed every other possibility. An accurate diagnosis before you buy any parts is the single best way to keep your total cost near the $80 to $250 range rather than accidentally landing at $1,000.

Can you drive with P0855?

In most vehicles, the car remains driveable after P0855 sets. You may notice reduced performance, a disabled auxiliary system, or slightly worse fuel economy, but the engine will typically keep running. That said, do not dismiss it just because the car feels normal. If the associated fault causes stalling, prevents the transmission from shifting properly, or triggers warnings related to braking or steering assist, treat it as a priority repair. Otherwise, plan to address it within the next few weeks before something else in the circuit fails.