P0787 — Shift Timing Solenoid A Low

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 P0787 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 a low 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 P0787 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0787 (parts and labor, USD, independent shop rates): Control module repair: $300–$1,000; Replace the faulty sensor or actuator: $150–$500; Repair wiring or connectors: $80–$250. Overall, fixing P0787 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 much does it cost to fix P0787?

Control module repair — $300–$1,000; Replace the faulty sensor or actuator — $150–$500; 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.

What is the most common cause of P0787?

The most common causes are: poor ground connection, blown fuse feeding the circuit, faulty sensor or actuator of the affected circuit.

What are the symptoms of P0787?

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

Will P0787 clear itself?

Sometimes P0787 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.

What does OBD2 code P0787 mean?

Shift Timing Solenoid A Low (P0787): 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, blown fuse feeding the circuit, faulty sensor or actuator of the affected circuit.

P0787 is a powertrain diagnostic trouble code that specifically refers to a low electrical signal condition in the shift timing solenoid A circuit. This solenoid is an electrohydraulic component inside your automatic transmission responsible for controlling the timing and feel of gear shifts. When the engine control module (ECM) or transmission control module (TCM) detects that the voltage or resistance reading from this solenoid falls below the manufacturer's specified threshold, it logs P0787 and turns on the Check Engine Light.

Your vehicle's computer monitors the shift timing solenoid circuit constantly while you drive. The module expects to see a specific voltage range during normal operation. When that signal drops outside acceptable parameters for a set number of consecutive drive cycles—indicating the solenoid isn't receiving adequate electrical input or isn't actuating properly—the system flags the fault. The stored freeze frame data captures the exact operating conditions at the moment the problem occurred, giving you a precise snapshot of engine RPM, load, coolant temperature, and vehicle speed to work from during diagnosis.

Symptoms of P0787

The Check Engine Light illuminates on the dashboard.
The transmission may enter failsafe or "limp mode," restricting operation to a single gear or limiting shift ranges to protect internal components.
Gear shifts feel delayed, harsh, or erratic compared to normal operation.
Fuel economy drops noticeably because the transmission cannot shift optimally.
The affected system operates intermittently or fails to activate entirely, depending on the severity of the electrical fault.

Common Causes of P0787

A weak or corroded ground connection supplying the shift timing solenoid circuit.
An open circuit, short-to-ground, or damaged wiring harness preventing proper electrical flow.
The shift timing solenoid itself has failed internally and cannot modulate hydraulic pressure correctly.
The transmission control module has a driver fault and cannot command the solenoid properly.
A blown fuse or fusible link feeding power to the solenoid circuit has interrupted voltage supply.

How to Diagnose P0787

Connect an OBD2 scanner, verify P0787 is stored, and record all freeze frame data—this tells you exactly what the engine was doing when the fault triggered.
Pull any additional stored trouble codes. Related codes in the transmission system often point to the true underlying cause. Also search manufacturer TSBs (technical service bulletins) for your specific make and model—some P0xxx codes have documented factory fixes or software updates available through the manufacturer website or NHTSA.
Perform a thorough visual inspection of the wiring harness and connectors routed to the transmission case. Look for cracked insulation, chafing from contact with metal surfaces, water intrusion, corrosion at the pins, and any signs of heat damage.
At the solenoid connector, use a multimeter to verify reference voltage is present, ground continuity is solid, and the signal wire shows appropriate resistance values within spec.
With the connector attached, wiggle and flex the harness while monitoring live data on your scanner—a dropping or intermittent signal confirms a broken wire or loose terminal.
Clear the code, then drive through a complete drive cycle that reproduces the freeze frame conditions (same RPM, load, temperature, and speed). If P0787 returns, the fault is confirmed and you have narrowed the circuit.

Repair Options and Costs

P0787 is typically addressed by replacing or repairing one of three areas:

Wiring or connector repair: $80–$250. Most cost-effective option when the issue is a damaged harness, corroded terminals, or poor ground—you're only paying for labor and minimal parts.
Shift timing solenoid replacement: $150–$500. The solenoid itself fails relatively often due to internal winding burnout or hydraulic contamination. This includes parts and standard labor at an independent shop.
Control module repair or replacement: $300–$1,000. When the TCM or ECM has an internal driver failure, module-level repair or a remanufactured unit becomes necessary—it's the most expensive scenario.

Overall, fixing P0787 typically costs between $80 and $1,000 depending on which component is at fault. An accurate diagnosis before purchasing parts always saves money; the control module replacement scenario is the least common cause and should be ruled out last.

Driving Safety Verdict

P0787 carries a short-term severity rating. Most vehicles remain drivable when this code is active, though you may experience reduced performance, limited gear selection, or noticeably higher fuel consumption. If the transmission enters limp mode, the car can still move but should be treated as urgency—continue driving only to reach a repair facility. Watch for stalling, no-start conditions, or any brake/steering warnings, which would elevate this to an immediate safety concern.