P0740 on 2012-2019 Fiat 500: Torque Converter Clutch Circuit Fixes

What's Unique About the 2012-2019 Fiat 500

For the 2012-2019 Fiat 500 sold in North America, automatic transmission models are equipped with an Aisin AW6F25 6-speed automatic transmission, not the Chrysler 62TE or Dualogic automated manual found in other markets or FCA vehicles. This is a crucial distinction, as diagnostic approaches and parts differ. The provided TSB #9004009 for the 62TE transmission, while not directly applicable, offers a relevant diagnostic pattern: if the solenoid circuit tests fine, the torque converter itself is the likely culprit. On the Aisin AW6F25, the TCC solenoid is a common failure point, but an internal torque converter failure is also a significant possibility, especially after ruling out fluid and electrical issues.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on
• Vehicle shudders or vibrates at steady speeds, especially during gentle acceleration below 20 mph.
• Engine RPMs are higher than usual at highway speeds
• Reduced fuel economy
• Harsh or delayed shifting
• Engine may stall when coming to a stop
• Transmission may feel like it's slipping

Most Likely Causes

1. Low or Contaminated Transmission Fluid 🔴 High Probability → Shop Transmission Assembly The transmission is a sealed unit without a dipstick, making fluid level checks less common for owners and leading to issues going unnoticed. Using the incorrect fluid is also a common error.
   How to confirm: The fluid level and condition must be checked by a mechanic via the fill and check plugs on the transmission case. The fluid should be red and clear, not brown, black, or burnt-smelling. The correct fluid is a specific type for Aisin transmissions, such as Mopar AW-1 or an equivalent, NOT ATF+4.
   Typical fix: Perform a transmission fluid drain and fill with the correct type of fluid specified for the Aisin AW6F25 transmission. 🎬 See this walkthrough on how to replace Fiat transmission fluid.
   Est. part cost: $80-$150
2. Faulty Torque Converter Clutch (TCC) Solenoid 🔴 High Probability → Shop Automatic Transmission Torque Converter The solenoid is an electronic part submerged in hot fluid, making it susceptible to failure over time from heat cycles and potential fluid contamination. It is often called a variable force solenoid (VFS).
   How to confirm: A technician can test the solenoid's resistance with a multimeter to see if it's within spec (e.g., a similar Volvo application specifies 12-18 ohms). A professional scan tool can also be used to command the solenoid on and off to check its response.
   Typical fix: Replace the TCC solenoid. This is often done by dropping the transmission pan and accessing the valve body where the solenoid is located.
   Est. part cost: $80-$200
3. Damaged Wiring or Connectors 🟡 Medium Probability The wiring harness to the transmission is exposed to road debris, moisture, and heat, which can cause corrosion or physical damage over time. Wires can become frayed or pins can push back in the main connector.
   How to confirm: Visually inspect the wiring harness leading to the transmission for any frayed wires, corrosion in the connectors, or loose pins. A continuity test can be performed on the TCC solenoid circuit from the TCM connector to the transmission connector.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the faulty connector.
   Est. part cost: $20-$100
4. Internal Torque Converter Failure 🟡 Medium Probability → Shop Automatic Transmission Torque Converter While less common than solenoid failure, the diagnostic logic for similar FCA vehicles (TSB #9004009) points to a failed torque converter if the solenoid is good. Technicians with experience on similar transmissions report that replacing the solenoid is often a temporary fix, with the true culprit being a worn internal clutch inside the torque converter.
   How to confirm: This is typically diagnosed after all other possibilities (fluid, solenoid, wiring) have been ruled out. A technician may analyze transmission data for excessive slip when lock-up is commanded. Finding excessive metal shavings in the transmission pan during a fluid service is a strong indicator.
   Typical fix: Replace the entire torque converter, which requires removing the transmission from the vehicle.
   Est. part cost: $450-$800

Rare But Worth Checking

• Faulty Transmission Control Module (TCM): → Shop Transmission Assembly A TCM failure is rare, but it can cause a false P0740 code. This should only be considered after all other circuit components and mechanical parts have been thoroughly tested and confirmed to be working correctly.
• Clogged Valve Body Passages: → Shop Transmission Valve Body Debris from worn clutches or old fluid can clog the small hydraulic passages within the valve body, preventing the TCC solenoid from properly controlling the clutch, even if the solenoid itself is functional.

Diagnosis Steps

1. Scan the vehicle's computer for P0740 and any other related transmission codes, like P0700 or P0741.
2. Check the transmission fluid level and condition. This must be done by a professional as there is no dipstick. Ensure the correct fluid (e.g., Mopar AW-1 equivalent) is being used.
3. Inspect the transmission wiring harness and main connector for any visible damage, corrosion, or loose pins.
4. Using a professional scan tool, monitor live data for TCC slip RPM to see if the clutch is attempting to engage when commanded.
5. Test the resistance of the TCC solenoid at the transmission connector. Compare the reading to the manufacturer's specifications (similar applications are 12-18 ohms, though some Aisin solenoids are lower, around 5.6 ohms). An open or shorted reading indicates a failed solenoid or internal wiring.
🎬 Watch: How to test transmission solenoids using a multimeter.
6. If accessible, command the TCC solenoid on and off with a scan tool while listening for an audible click from the solenoid.
7. If the solenoid and wiring test good, but symptoms persist, the problem is likely a clogged passage in the valve body or an internal failure of the torque converter itself.

Parts You'll Likely Need

• Torque Converter Clutch (TCC) Solenoid — This is the most common electrical component to fail in the circuit, leading directly to a P0740 code. It is located on the valve body.
  Trusted brands: Mopar, Rostra, Dorman
  OEM price range: $150-$250
  Aftermarket price range: $80-$150
• Automatic Transmission Fluid (OEM #Mopar AW-1 or equivalent) — Low or degraded fluid is a primary cause of many transmission issues. The Aisin transmission in the Fiat 500 requires a specific fluid, NOT ATF+4.
  Trusted brands: Mopar AW-1, Idemitsu TLS-LV, AISIN ATF-0WS
  OEM price range: $20-$30 per quart
  Aftermarket price range: $15-$25 per quart
• Torque Converter — If the solenoid and wiring are confirmed to be good, the torque converter's internal clutch has likely failed. This is a common point of failure after other, simpler causes are ruled out.
  Trusted brands: Mopar, LuK, Transtar
  OEM price range: $600-$900
  Aftermarket price range: $450-$700

Related Codes That Often Appear With This One

• P0700 — This is a generic transmission fault code that simply indicates the TCM has stored a fault. It is almost always present alongside more specific transmission codes like P0740.
• P0741 — This code indicates 'TCC Circuit Performance or Stuck Off,' which is a closely related mechanical/hydraulic issue, whereas P0740 points specifically to an electrical circuit fault.
• P2764 — Mentioned in TSB #9004009 alongside P0740 for other FCA vehicles, this code also relates to the TCC pressure control solenoid circuit, indicating a comprehensive TCC system problem.

Technical Service Bulletins (TSBs) & Recalls

• 9004009: While written for the 62TE transmission not found in the 500, it provides valuable diagnostic logic, suggesting torque converter failure if the TCC solenoid tests okay for code P0740. This pattern is often seen in other transmissions as well.

Platform-Specific Known Issues

• The provided TSB #9004009 for Fiat-Chrysler vehicles with the 62TE transmission states that if the TCC solenoid is functional, a P0740 code is indicative of a torque converter failure. While the Fiat 500 uses a different (Aisin AW6F25) transmission, this diagnostic logic is often still applicable.

Mechanic-Grade Diagnostic Values

• Torque Converter Clutch (TCC) Solenoid Resistance — expected: Approximately 5.6 Ohms. General aftermarket solenoids can range from 10-30 Ohms.. Failure: A reading of infinite resistance (open circuit) or zero resistance (short circuit).

Scan Tool Commands That Help

• AlfaOBD: Transmission Actuator Tests / Calibration — After checking wiring, use a tool like AlfaOBD to command the TCC solenoid on and off to verify its mechanical operation (listening for a click). It may also offer gearbox calibration routines that can help diagnose or reset transmission control logic after a repair.

Wiring & Ground Locations

• Main Battery Ground Cable — Runs from the battery negative terminal, connects to the car body (often below the battery tray), and continues to a bolt on the engine block or transmission case.. This cable can corrode internally without visible external signs. A high-resistance ground can cause a variety of intermittent and difficult-to-diagnose electrical faults, including incorrect sensor readings or insufficient voltage for solenoids, potentially triggering a P0740 code.
• T20 / T30 Relays — In the main fuse box located in the engine bay, near the battery.. These relays can be part of the power supply circuit for the automatic transmission controls. A faulty relay could interrupt power to the TCM or the solenoids it controls, leading to circuit codes like P0740.

"I Checked Everything" — The Actual Cause

• A common pattern reported by technicians for similar transmissions is replacing the TCC solenoid for a P0740 code, only for the code to return within a few days or weeks. The actual root cause is often a mechanically failing torque converter clutch. A new solenoid is strong enough to briefly overcome the mechanical issue, but it soon fails again, making the solenoid replacement a temporary 'band-aid' rather than a permanent fix.

Model Year Variations Within This Range

• 2012-2019: The North American Fiat 500 uses a conventional 6-speed Aisin automatic transmission, which was a specific addition for this market. This is fundamentally different from the 'Dualogic' automated manual transmission found in many European models, which has its own unique set of common failures and diagnostic procedures.