P1508 — Auxillary Speed Sensor Fault

How do I diagnose P1508 myself?

Start with a scan: confirm P1508, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the auxillary speed sensor, and verify the suspect component against live data before buying parts.

How much does it cost to fix P1508?

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

What is the most common cause of P1508?

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

Will P1508 clear itself?

Sometimes P1508 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 P1508?

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.

Your scan tool just returned P1508, and you're wondering what that means for your vehicle. P1508 indicates the powertrain control module has detected that the auxiliary speed sensor circuit is operating outside its factory-calibrated parameters. When the PCM monitors sensor and actuator inputs across multiple drive cycles and finds values drifting beyond acceptable thresholds, it triggers this fault.

The auxiliary speed sensor feeds critical data to various vehicle systems. When it fails or sends unreliable signals, the control unit cannot properly manage functions that depend on accurate speed information. Alongside storing the fault code, the module captures a freeze frame snapshot showing engine RPM, calculated load, coolant temperature, and vehicle speed the instant the problem occurred. That snapshot is your best starting point for diagnosis.

Symptoms of P1508

When P1508 sets, you may notice one or more of the following:

• Check Engine Light illuminates on the dashboard
• The affected system operates inconsistently or stops working entirely
• Fuel economy drops compared to normal driving habits
• The vehicle may enter reduced-power or limp-home mode depending on which component is involved
• Reduced overall driveability in some cases

Common Causes of P1508

The root cause of P1508 typically falls into one of these categories, listed from most to least frequent:

• The auxiliary speed sensor or its related actuator has failed internally
• An inline fuse protecting the circuit has blown
• Corrosion, looseness, or physical damage at the sensor connector
• A broken, chafed, or shorted wire within the harness
• Insufficient ground at the component or control module
• The control module's output driver for that circuit has failed

How to Diagnose P1508

Follow this systematic approach to isolate the fault without replacing parts unnecessarily:

1. Connect an OBD2 scanner, record that P1508 is present, and save the freeze frame data — it reveals what the engine was doing when the fault triggered.
2. Look for any related diagnostic trouble codes. Secondary codes often point directly to the failed component. Check manufacturer TSBs for your specific make and model, as many P0xxx codes have documented factory fixes or calibration updates.
3. Perform a hands-on inspection of the wiring and connectors tied to the auxiliary speed sensor. Look for broken insulation, bent pins, moisture intrusion, or loose plugs.
4. With a multimeter, verify reference voltage, ground integrity, and signal continuity at the sensor connector against factory specifications.
5. Monitor live data from the sensor while gently moving the harness. Any dropouts or erratic readings confirm intermittent wiring failures.
6. Clear P1508 after repairs, then complete a full drive cycle that replicates the freeze frame conditions. The code should not return if the fault is genuinely fixed.

Repair Options and Costs for P1508

Repair costs vary widely depending on which part is actually at fault. Here are typical scenarios using independent shop labor rates in USD:

• Repair wiring or connector issues: $80–$250
• Replace the faulty sensor or actuator: $150–$500
• Repair or replace the control module: $300–$1,000

Total Cost to Fix P1508

The full repair bill for P1508 typically lands between $80 and $1,000 depending on the actual failure. Always diagnose before buying parts — the most expensive scenario (control module replacement) is rarely the culprit, and starting with visual and electrical checks saves money.

Driving Safety Assessment for P1508

P1508 carries a short-term severity rating. Most vehicles remain driveable, though you might experience lower fuel efficiency, disabled auxiliary functions, or automatic power reduction. If the car stalls unexpectedly, fails to start, or triggers brake and stability warnings, treat it as an emergency. Otherwise, schedule the repair at your earliest convenience.

Related OBD2 Codes

• P1500: Secondary Switch Solenoid Circuit Malfunction
• P1501: APLSOL Solenoid Circuit Malfunction
• P1502: RCNT Solenoid Circuit Malfunction
• P1503: SPCUT Solenoid Circuit Malfunction
• P1504: TCSPL Solenoid Circuit Malfunction
• P1505: Vehicle Speed Sensor Intermittent