P1742 — Lockup Solenoid System

For Ford vehicles

torque converter clutch enable solenoid valve locked on

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 P1742 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 lockup solenoid system 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 P1742 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P1742 (parts and labor, USD, independent shop rates): Replace the faulty sensor or actuator: $150–$500; Control module repair: $300–$1,000; Repair wiring or connectors: $80–$250. Overall, fixing P1742 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 does OBD2 code P1742 mean?

Lockup Solenoid System (P1742): 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 corroded, loose or damaged connector, control module driver fault, open or shorted wiring in the circuit.

What are the symptoms of P1742?

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

What is the most common cause of P1742?

The most common causes are: corroded, loose or damaged connector, control module driver fault, open or shorted wiring in the circuit.

How do I diagnose P1742 myself?

Start with a scan: confirm P1742, 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.

How much does it cost to fix P1742?

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

When your OBD2 scanner pulls code P1742, it means the vehicle's control unit has detected a problem with the lockup solenoid system. Specifically, the module is reporting that one or more circuits within this system are running outside their expected parameters. P1742 falls under the powertrain category, meaning it touches both engine and transmission management systems.

The lockup solenoid plays a role in how your transmission behaves, particularly during highway driving. When conditions are right, this solenoid engages the torque converter lockup clutch, effectively linking the engine directly to the transmission. This reduces slip, improves efficiency, and cuts fuel consumption. The engine control module (ECM) or transmission control module (TCM) constantly monitors the solenoid's electrical circuits through sensor readings and actuator feedback. When those readings drift beyond factory-set limits—typically across multiple drive cycles—the module logs P1742 and captures a freeze frame snapshot showing RPM, engine load, coolant temperature, and vehicle speed at the moment of failure. That snapshot is your starting point for diagnosis.

Understanding why P1742 triggers requires knowing how the system works. The control module sends commands to the lockup solenoid and expects specific voltage signals in return. A healthy circuit shows consistent values within a narrow band. When wiring problems, connector failures, or component faults disrupt that signal path, the module recognizes the anomaly and sets the code. The underlying cause could be as simple as corroded pins in a connector or as complex as an internal failure inside the transmission control unit itself.

Symptoms of P1742

The Check Engine Light will illuminate once P1742 is stored. Depending on which specific circuit is affected and how the manufacturer programmed the transmission logic, the vehicle may enter limp mode—restricting gears or reducing performance to protect drivetrain components. Fuel economy often suffers because the torque converter cannot lock up efficiently, causing excess slip. In some cases, the lockup function operates sporadically or quits entirely, leaving you with an otherwise functional but less efficient transmission.

Common Causes

The most frequent culprit behind P1742 is damaged or degraded wiring in the solenoid circuit—cracked insulation, broken strands, or chafing from nearby components can create open circuits or shorts. Corroded, loose, or physically damaged connectors prevent reliable electrical contact and are especially common in vehicles exposed to moisture or road salt. A failing lockup solenoid sensor or actuator can also trigger this code when its internal resistance drifts out of specification. Poor ground connections disrupt the complete circuit path and cause erratic readings. Finally, an internal fault within the control module itself—specifically the driver circuit that handles the solenoid—can set P1742 even when all external wiring checks out.

How to Diagnose P1742

Begin by connecting a quality OBD2 scanner and confirming P1742 is present. Record the freeze frame data before clearing anything—this tells you exactly what conditions existed when the fault occurred. Next, research any technical service bulletins (TSBs) specific to your make, model, and model year. Search using your VIN on the manufacturer website or through NHTSA, as many transmission-related codes have documented factory fixes or software recalibrations. After reviewing TSBs, perform a thorough visual inspection of the wiring harness and connectors associated with the lockup solenoid. Look for damaged wires, corroded terminals, melted insulation, or loose plugs. Use a multimeter to check reference voltage, ground integrity, and signal continuity at the component itself. Perform a wiggle test on the harness while monitoring live data—if the signal drops or fluctuates during movement, you've found a broken wire or intermittent connection. Once inspections are complete, clear the code and drive the vehicle through a complete drive cycle, recreating the conditions from the freeze frame. If P1742 returns, the fault is confirmed and repairs can proceed.

Repair Options and Costs

Repair costs for P1742 vary significantly depending on which component actually failed. Wiring harness repair or connector replacement typically runs $80 to $250 including parts and labor. Replacing a faulty lockup solenoid sensor or actuator generally costs between $150 and $500. If the control module itself requires repair or replacement, expect to spend $300 to $1,000. Always pursue the least expensive probable cause first—wiring issues are far more common than module failures, and proper diagnosis prevents unnecessary part purchases.

Driving Safety Verdict

Most vehicles with P1742 remain drivable, though you may notice reduced fuel economy, transmission hesitation, or limited gear availability. If the car develops stalling, failure to start, or warning lights related to brakes or steering, treat the situation as urgent and seek repairs immediately. Otherwise, schedule diagnosis and repair at your earliest convenience to restore full efficiency and prevent potential transmission damage from prolonged limp-mode operation.