Fix P0740: Mechanic’s solutions that WORKED

The Code P0740: Torque Converter Clutch Circuit Malfunction points out a fault in the torque converter clutch circuit, and most likely is caused by issues related to the torque converter clutch solenoid or its associated wiring.

P0740 quick overview

Meaning	P0740: Torque Converter Clutch Circuit Malfunction
Is it serious?	Yes, the torque converter plays a vital role in the operation of the automatic transmission. Issues with the torque converter clutch circuit can lead to reduced fuel efficiency, erratic shifting, and potential long-term damage to the transmission if not addressed.
Possible causes	– Damaged or corroded TCC connector. – Malfunctioning TCC solenoid. – Wiring harness issues at the transmission, possibly due to moisture or being too loose. – Faulty or worn valve bodies in the transmission, especially the TCC pressure regulator. – Electrical issues in the circuit that controls the TCC solenoid.
How to diagnose?	Visual Inspection: Begin by checking the TCC connector for any visible signs of damage or corrosion. Check for Technical Service Bulletins (TSBs): Use dealership information to check if there are any TSBs related to the P0740 code for your vehicle model. Test the TCC Solenoid: Verify the operation of the TCC solenoid. It should show a proper resistance value and should actuate when applied with power. Inspect Wiring Harness: Examine the wiring harness at the transmission for any signs of damage, wear, or moisture. Evaluate Electrical Circuits: Use a multimeter to check the integrity and voltage levels of the circuits controlling the TCC solenoid. Examine Valve Body: For vehicles with a history of transmission work, inspect the valve bodies, especially the TCC pressure regulator, for wear or malfunction. Consult Expertise: If issues persist, it might be beneficial to consult a transmission specialist or the vehicle’s dealership for further insight.
What is Torque converter?	A torque converter is a fluid-filled component in an automatic transmission that transfers engine power to the transmission, allowing the engine to keep running even when the vehicle is stopped. It acts like a bridge between the engine and the transmission, providing smooth acceleration.

How to fix P0740 – learn from mechanics

I looked into P0740 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Volvo

Vehicle Information 2003 Volvo V40 1.9L

Issue + Repair History

• Check engine light displayed codes: P0740 and P0335
• Installed used transmission assembly, followed by two successful road tests
• Codes reappeared in history after one lengthy drive by the customer

What are people suggesting to fix the issue

• P0740 is a TCM code indicating issues with the lock-up function which could lead to harsh gear shifting, warning lamp for the transmission flashing, and no lock-up function.
• The possible sources for P0740 include poor quality transmission fluid and mechanical faults in the transmission.
• P0335 is an ECM code pointing to an engine speed (RPM) sensor signal missing or showing an intermittent fault. This could cause the engine to misfire.
• The potential causes for P0335 include issues with the signal cable (open circuit, short circuit to ground, or short circuit to supply voltage), faulty engine speed (RPM) sensor, loose connections, damaged flywheel.
• Changing the fluid and filter and ensuring the use of only Volvo-approved fluid.

What was the final fix

• The mechanic installed another used transmission which resolved the problem, suggesting the issue was in the transmission from the beginning.

Case #2: Chrysler

Vehicle Information 1998 Chrysler Sebring LXi 2.5L

Issue + Repair History

• Displayed multiple codes from different scanners: 08, 26, P0700, and P0740
• Code P0740 indicates lock up control out of range
• CVI readings: lr 54, 2-4 50, od 145, ud 66. The OD reading at 150 is considered too high.
• Previously replaced TCM and solenoid pack.

What are people suggesting to fix the issue

• A CVI of 150 for OD suggests a worn-out component, possibly indicating the need for a rebuild.
• CVI at 150 on OD might mean clutch pack is out of specification due to worn clutches or broken snap ring.
• Replacing the output sensor might be a solution.
• High OD CVI might be caused by a broken snap ring.
• CVI readings are clutch volume indices which measure clutch fill time; a high CVI of 145 indicates the OD clutch has excessive clearance or there’s a fluid leak to the OD clutch, likely requiring further inspection and repair.

What was the final fix

• The problem was not with the solenoid pack; it was the valve body. A valve was hanging up and not closing a switch in the solenoid pack.

Case #3: Dodge

Vehicle Information 1998 Dodge Ram 1500 ST 5.2L

Issue + Repair History

• Vehicle displayed a check engine light.
• Code: P0740 torque converter solenoid circuit failure.
• Owner observed a possible intermittent RPM change while driving.
• All three solenoids and a sensor in the transmission were replaced, which seemed to resolve the RPM change issue.
• A week after the repairs, the check engine light returned with the same code, even though the transmission felt fine.

Observations

• At 55 MPH, when the vehicle shifts into 4th and then overdrive, there’s a 150 RPM drop.
• Tapping the brake pedal causes a 200 RPM increase.
• Holding down the brake pedal on the freeway leads to an RPM increase of 200, but the transmission still shifts back into overdrive.
• Code P0740 was identified as a torque converter issue, not a solenoid issue.

Responses and Suggestions

• Respondent 1: The P0740 code is seen as a performance code, suggesting a possible failed torque converter. It was recommended to bypass the radiator cooler and add an external or ensure it’s clean with a good flow rate.
• Respondent 2: The problem could be due to excessive converter clutch slippage, and a rebuild might be required to address it.
• Respondent 3: P0740 suggests an issue with the converter clutch operation. It might be necessary to replace both the torque converter and the front pump.
• Respondent 4: Torque converter clutch failures are common. If there’s evidence of converter clutch in the cooler, that’s likely causing the code.
• Respondent 5: The converter clutch seems to be slipping, indicating that the torque converter may need replacement. However, other worn components could be the root cause.
  
  The final fix wasn’t performed as the customer didn’t want to spend money on the vehicle.

Case #4: Dodge

Vehicle Information 1994 Pontiac Trans Sport 3.8L

Issue + Repair History

• Transmission issue with the 4L60E (later corrected as 4T60E) transmission.
• Initial symptom was that after the first shift sequence, the vehicle lost both the TCC lockup and 4th speed.
• This issue occurred whether the vehicle was hot or cold.
• To reset, the engine had to be turned off and restarted.
• A decision was made to rebuild the transmission. This involved inspecting the valve body, replacing the harness, PWM and TCC solenoid, and the torque converter.
• The van functioned correctly for a week but then reverted to the original issue.

Observations and Tests

• After re-encountering the problem, voltage checks at the two solenoids revealed no drop.
• Inquiry was made about the feasibility of plugging in a pressure gauge for the TCC.
• A prior repair history noted a new harness being installed at 80,000 KM for the same issue.

Updates and Final Resolution

• Based on advice and suggestions, the valve body was removed and re-inspected.
• The TCC regulator valve was found to be worn (unclear how it was missed during the initial overhaul).
• The definitive fix for the problem was to either replace the valve body or install a kit from Sonnax. The latter option was chosen.
• The TCC pressure regulator was notably in bad shape.
• With the new kit from Sonnax, the van’s issues were resolved.

Relevant Test Results

• Code P740 indicated TCC slip.
• TCC solenoid tests showed proper application and resistance.
• PWM solenoid resistance was also within normal range.

Case #5: Hyundai

Vehicle Information 2000 Hyundai Sonata 2.4L Electronic

Issue

• Customer experienced sporadic high rpms while driving.
• The problem wasn’t consistently reproducible; the car functioned normally during test drives.
• A code of PO740A (TCC circuit malfunction) was triggered.

Inquiries

• Uncertainty about the code PO740A in relation to a Hyundai vehicle.
• Questions regarding the Hyundai 100,000-mile warranty coverage.

Resolution

• The TCC (Torque Converter Clutch) connector at the transmission was found corroded.
• After cleaning the connectors and repairing the terminals, the vehicle functioned correctly.