Fix P0780: Mechanic’s solutions that WORKED

The P0780: Shift Malfunction signifies a problem with the shifting process in your vehicle’s transmission. It could be due to several reasons like internal damage to the transmission, issues with the control module that manages gear shifting, or problems with the shift solenoids that facilitate gear changes. This code often comes with noticeable symptoms such as erratic shifting or the vehicle struggling to change gears.

P0780 quick overview

Meaning	P0780: Shift Malfunction
Is it serious?	Yes, this code is serious as it can indicate significant transmission issues, potentially affecting the vehicle’s drivability.
Possible causes	– Internal transmission mechanical problems – Faulty or failing transmission control module (TCM) – Issues with the shift solenoids – Low or dirty transmission fluid – Electrical problems in the transmission circuit
How to diagnose?	Check Transmission Fluid: Verify the level and condition of the transmission fluid. Inspect Wiring and Connectors: Look for any damaged or loose connections in the transmission circuit. Test Shift Solenoids: Perform tests on the shift solenoids to check their operation. Scan for Additional Codes: Use a diagnostic scanner to check for other related transmission codes. Inspect Internal Transmission: Consider inspecting the transmission internally for any mechanical issues. Evaluate TCM: Assess the condition and functionality of the transmission control module.

How to fix P0780 – learn from mechanics

I looked into P0780 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: Honda

Vehicle Information: 2003 Honda Pilot EX 3.5L

Issue + Repair History:

• Vehicle recently had major repair at body shop, including engine and transmission removal.
• After reinstallation, transmission hesitated to shift to second gear.
• Check engine light appeared, and the transmission entered limp mode.
• Code PO780 (Shift malfunction) was identified.

Suggestions to Fix Issue:

• Check connections and for any pinched wires at shift solenoid A and pressure control solenoids.
• If the vehicle shifted fine before the accident, it should work properly after ensuring solenoids are not damaged.
• Consider replacing shift solenoid “A” and A/T clutch solenoid “A & B” as an assembly.
• Clear codes first (e.g., pull fuse 13 under the dash for 30 seconds) and replace solenoids if PO780 returns.
• Inspect all shift solenoid connectors for damage, especially if the engine lifting could have caused them to hit the frame.
• Check for correct wire routing and potential mix-up of solenoids due to similar size and different colors.
• Inspect the driver’s side under-dash fuse box, specifically fuse #6 (15A), which feeds power to the shift solenoids.
• Look for damaged connectors on solenoids, which can occur during accidents or transmission removal and reinstallation.

Final Fix:

• The vehicle required a new transmission due to internal problems apparently caused by the accident.

Case #2: Mercedes

Vehicle Information: 2015 Mercedes-Benz ML250 Bluetec 4Matic 2.1L Diesel

Issue + Repair History:

• Vehicle brought in for 46,500-mile service.
• Inquiry about the need for a bleeding procedure on the fuel filter.
• Question on whether to remove the entire air filter box and disconnect the PCM and harness to replace the air filter.

Suggestions to Fix Issue:

• For the air filter replacement, peel back the module attached to the air filter housing instead of removing it entirely.
• Leave the CDI module plugged in and pry the top cover to the rear of the engine bay for air filter replacement.
• For the fuel filter, it’s recommended to turn the key to position 2 a few times to fill the new fuel filter.
• Advised to install new clamps when replacing the fuel filter.
• No need to remove the PCM, just safely unclip the plastic fasteners guarding the harness to access the tox screw for the air filter.
• The diesel filter is a self-prime system, so there are no concerns about needing a bleeding process.

Final Fix:

• Vehicle fixed with guidance from provided WIS (Workshop Information System) documents and community suggestions, specifically on handling the air and fuel filter without extensive disassembly.

Case #3: Acura

Vehicle Information: 2003 Acura TL Type-S 3.2L

Issue + Repair History:

• Recently installed a water pump and timing belt.
• Car returned with bucking on the highway.
• Scanner showed codes P1739, P0730, P0780.
• Oil found in 3rd clutch pressure switch, which was replaced.
• Problem persisted, including issues with reverse gear (vehicle moved forward before going into reverse).

Other Test Results:

• P1739: Bad 3rd clutch pressure switch.
• P0730: Incorrect gear ratio.
• P0780: Shift malfunction.

Suggestions to Fix Issue:

• Check with Acura for potential warranty coverage on the transmission.
• Several similar cases were warrantied by Acura due to known transmission issues.
• Internal transmission failure is likely, including issues with the torque converter clutch or valve body.
• Verify warranty status based on vehicle’s VIN and mileage.

Final Fix:

• Referred to a service bulletin (02-027) indicating warranty extension for automatic transmission on certain Acura models, including 3.2TL Type S.
• Vehicle sent to the dealer for repair under warranty, addressing the known issue with the 3rd gear clutch pack.

Case #4: Nissan

Vehicle Information: 2006 Nissan Maxima SL 3.5L

Issue + Repair History:

• Replaced transmission with a factory unit from Nissan due to code P0780 (shift malfunction).
• After replacement, trouble initializing the TCM (Transmission Control Module).
• Used a Snap-On Verus scanner for the process but faced issues with test timing out despite meeting conditions (transmission in park, operating temperature).

Suggestions to Fix Issue:

• A suggestion to use a Consult II tool, as some cars might need it for successful initialization.
• Recommendation to take the TCM from the old transmission and install it on the new one.
• Check if initialization is attempted with the key on, engine off (KOEO).

Final Fix:

• The issue was resolved with the newest version of the Snap-On scanner which successfully initialized the TCM.
• The vehicle is now shifting properly.
• Planning to purchase the newest scanner to avoid similar issues in the future.

Case #5: Mazda

Vehicle Information: 2012 Mazda 3 i 2.0L

Issue + Repair History:

• Installed a used engine.
• Post-installation, transmission had issues: would engage in reverse, severe hesitation in forward gear, and lack of pulling power.
• Delayed engagement from stops after vehicle sat over the weekend.
• Codes present: ABS U0401, IC U0402, TCM P0731, P0732, P0733, P0780, P1738.
• Grounds cleaned and confirmed to be tight and good.

Suggestions to Fix Issue:

• Check and double-check all grounds, ensuring they are reinstalled correctly and making good contact. Clean mating surfaces and consider using a contact enhancer.
• Verify all connectors are making good contact; reinsert them several times with a contact enhancer if necessary.
• Check for any expanded female pins in connectors.
• Ensure no connectors got swapped, causing sensors to read incorrect ranges.
• Consider the possibility of a TCM failure.
• Check the engine’s running condition, particularly the crank sensor/pulse ring.
• Review engine and transmission actual values for plausibility in different conditions (key on engine off, at idle, etc.).
• Verify correct transmission fluid level and ensure the use of proper fluid, especially if any was lost during engine replacement.

Final Fix:

• The vehicle required a new transmission.
• The TCM was reflashed at Mazda, which resolved some issues, but the transmission lacked fifth gear.

Advice	Brief Description of Diagnostic Step
Check Transmission Ground Connections	Ensure all transmission ground connections are reinstalled correctly and making good contact. Clean mating surfaces.
Verify Connector Contacts	Check all relevant connectors for proper contact. Reinsert connectors multiple times if necessary, considering contact enhancer usage.
Assess for Potential Warranty Coverage	Investigate if the vehicle’s transmission issue might be covered under any existing warranties or service bulletins.
Consider TCM Issues	Evaluate the possibility of a Transmission Control Module (TCM) failure, especially if there are difficulties in initialization or shifting.
Review Previous Repair History	Take into account any recent repairs or replacements done on the vehicle that might relate to the transmission issue.
Check for Correct Fluid Level	Ensure the transmission fluid is at the correct level and the fluid used is appropriate for the vehicle.
Reprogram or Replace TCM if Necessary	If TCM issues are suspected, reprogram or replace the module after confirming it is the source of the problem.