The P0740 code is one of the more serious trouble codes you could see. When your vehicle’s torque converter clutch circuit isn’t working properly, you’ll have difficulty shifting between gears. This can lead to overheating, rough starts, and long-term engine damage.
Fixes for the P0740 trouble code are sometimes very easy, simple, and affordable. In other cases, they’re more significant and costly repairs. While the symptoms present in your car can help guide you, careful diagnosis is the only real way to determine which one you’re dealing with.
The design of your vehicle’s transmission will affect your diagnosis. Read on below for more information about this code and what’s required to diagnose and repair it.
P0740 Code Definition
P0740 Code Definition (Generic): Torque Converter Clutch Circuit Malfunction
P0740 Honda Code Definition: TC Clutch System Failure
P0740 Jeep Code Definition: TCC Circuit Fault
What Does P0740 Mean?
In modern vehicles with automatic transmissions, there is a torque converter between the transmission and the engine. This increases the torque output, giving more power to the rear wheels.
There is a fluid coupling device inside the torque converter. This is what actually connects the engine to the transmission. It multiplies the torque, equalizing the speeds. How much hydraulic fluid is in this coupling is controlled by the powertrain control module (PCM) via the transmission control module (TCM).
If the TCM detects a fault within the circuit operating the torque converter, the P0740 trouble code activates. While this is a generic powertrain code, applicable to all vehicle types, the specific fix may vary depending on your transmission. It’s important to check your manual for specific fixes before proceeding with any diagnosis.
The style of transmission build varies from one manufacturer to the next. Some use a TCC solenoid connected to the transmission case using wires and plugs. In other cases, the TCM is bolted directly to the transmission case, or it may be of a single unit. These differences in style are one reason you should look for specific fixes related to your vehicle.
What Are The Symptoms Of The P0740 Code?
There may be no drivability symptoms associated with the P0740 code (except the CEL). In most cases, though, you’ll experience one or more of the following:
- Activation of the check engine light
- Reduced fuel economy
- Transmission not shifting into/out of gear properly
- Harsh shifts
- Engine stalls
- Engine overheating
What Are The Causes Of P0740?
- Faulty torque converter solenoid
- Faulty torque converter
- Damage, shorts, or loose connections in the wiring harness
- Faulty engine coolant temperature sensor
- Faulty valve body
- Transmission fluid old, dirty, or too low
- Issue with the TCM or PCM
How Serious Is The P0740 Code?
The P0740 trouble code can be very serious, especially if you’re experiencing drivability symptoms. In some cases, your vehicle will stall or refuse to start when this code triggers, leaving you stranded. You should stop driving your car as soon as you notice the P0740 code, and have it repaired immediately to avoid further engine damage.
How To Diagnose And Fix The P0740 Code?
Tools you’ll need:
- Look for any technical service bulletins that exist for this code for your make and model. Follow any manufacturer-specific fixes outlined in these bulletins. They will likely fix your issue. If they don’t (or if none exist), continue with the general diagnosis and repair below.
- Scan your vehicle with the OBD2 scan tool, checking for other codes. You may see other transmission DTCs, including P0741-P0744, P2769, or P2770. If you see multiple transmission trouble codes, this likely indicates a failure in the electrical system.
- Check the transmission fluid. It should be bright and clear, typically a vibrant red in color. If it’s brown, black, cloudy, or has visible debris floating in it, you should replace it. Replace the filter, as well, and flush the system. Refill it with new transmission fluid, ensuring it’s fully filled.
- Inspect the transmission’s wiring harness. Replace any damaged wires you see. The wiring diagram in your manual will likely be especially helpful in determining whether all connections have been securely made. Reconnect any loose or disconnected wires you see, and make sure the connections themselves are uncorroded.
- Use a digital multimeter to check the continuity of the internal transmission wiring. Touch the positive and negative multimeter leads to the appropriate pins on the TCC solenoid. A resistance that reads OL (over limit) or one that’s very high indicates a fault. The TCC solenoid likely needs to be replaced.
- With the digital multimeter, test the wiring connecting the TCM to the transmission case. Turn the multimeter to ohms and connect the negative lead to your vehicle’s negative battery terminal, or another suitable ground. You should get an OL (over limit) or high resistance reading. If you don’t, there may be a short in the wiring.
- Should the code still not clear, test the function of the clutch and torque converter. You may need to replace one or both.
- If these repairs do not clear the code, you may have a more serious issue. In some cases, the transmission itself may need to be rebuilt. Other times, it could be an issue with the PCM or TCM. Either way, this is not a repair it’s recommended you do at home. Take your vehicle to a mechanic for further diagnosis.
Common Mistakes To Avoid While Diagnosing The P0740 Code
Don’t assume the torque converter is damaged when this code activates. There are a variety of causes for this code, including simple fixes like disconnected wires or needing more transmission fluid. Conduct a thorough diagnosis before replacing costly components.
Tips To Avoid P0740 In The Future
Proper transmission system maintenance is the best way to avoid P0740 and other transmission-related trouble codes. Check your transmission fluid regularly, refilling or replacing as necessary. Transmission fluid that’s dirty or too low can lead to a host of transmission issues, some of which are rather costly to replace. You’ll save yourself a lot of time and money by staying on top of your regular maintenance.