Fix P0894: Mechanic’s solutions that WORKED

The P0894: Transmission Component Slipping fault code is an important signal from your vehicle’s onboard diagnostics system, indicating a potential concern with transmission component slipping. While not an immediate cause for alarm, this code should not be ignored, as it can lead to more significant transmission problems if left unattended.

P0894 quick overview

Description	P0894: Transmission Component Slipping
Is it serious?	This code indicates a potential issue with transmission component slipping. While not an immediate breakdown, it can lead to transmission problems and reduced performance if left unaddressed.
Possible causes	– Low or contaminated transmission fluid – Faulty torque converter – Malfunctioning TCC (Torque Converter Clutch) solenoid – Wiring or electrical issues in the TCC circuit – Mechanical problems within the transmission
How to diagnose?	Check Transmission Fluid: Verify the transmission fluid level and condition. Ensure it’s at the correct level and not contaminated. Inspect Torque Converter: Examine the torque converter for any damage or wear that may be causing slipping. Test TCC Solenoid: Test the TCC solenoid to ensure it’s functioning correctly and receiving the proper electrical signals. Check Wiring and Connections: Inspect the wiring and connections in the TCC circuit for any damage or loose connections. Perform a Transmission Diagnostic: Use a diagnostic tool to perform a comprehensive transmission diagnostic to identify any mechanical issues.

How to fix P0894 – learn from mechanics

I looked into P0894 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: Chevrolet

Vehicle Information: 2006 Chevrolet Trailblazer EXT LT 4.2L

Issue + Repair History: The Chevrolet Trailblazer was experiencing a random PO894 code. The code did not reset after clearing and driving for a week. The customer reported the light coming on when exiting the freeway, with no noticeable transmission shifting issues. Transmission flush and filter replacement were performed as a first attempt at fixing the problem.

Other OBD2 Codes + Test Results: None mentioned.

Suggestions to Fix Issue:

1. Check for TCC Solenoid Cracks: Inspect the TCC solenoid for hairline cracks, especially on the “neck” of the solenoid.
2. Investigate TCC Regulator Apply Valve: The TCC regulator apply valve might be worn, causing incomplete TCC application, especially when the transmission warms up.
3. Consider Valve Body Replacement: Replacing the valve body with a remanufactured one from GM or reputable builders.
4. Replace TCC Valve: Replace the TCC valve using parts from a Transgo shift kit or Sonnax replacement valve if necessary.

Final Fix: The P0894 code issue was resolved by replacing the TCC solenoid based on community suggestions. The code did not return after the replacement, and the problem was considered fixed.

Case #2: Mazda

Vehicle Information: 2006 Mazda 6 i 2.3L

Issue + Repair History: The Mazda 6 had a bent conrod and a torn VVT actuator, leading to the replacement of the engine with a low-mileage used one. During the first road test after the engine swap, the transmission went into limp mode and set codes P0734 (gear 4 ratio incorrect) and P0894 (trans components slipping). A transmission flush and code clearing initially resolved the issue for about 10 miles, but the problem returned, and the transmission refused to engage in drive or reverse.

Other OBD2 Codes + Test Results: None mentioned.

Suggestions to Fix Issue:

1. Check Flex Plate: Ensure the flex plate is not mismatched and matches the engine’s specifications.
2. Inspect Torque Converter Connection: Verify that the torque converter is properly aligned with the pump when the engine and transmission were bolted together.
3. Ask About Previous Transmission Behavior: Inquire with the customer about how the transmission behaved before the engine failure.
4. Consider Transmission Replacement: Due to the random functionality of the transmission and line pressure being in spec, it’s suggested to investigate a potential module or electrical issue before opting for a transmission replacement.

Final Fix: The issue was resolved by replacing the transmission with a new used one. No damage was noticed to the torque converter drives. It’s assumed that the original transmission was on the edge of failing, and the transmission flush may have exacerbated the issue. The customer ended up with a complete low-mileage drivetrain in their Mazda 6.

Case #3: GMC

ehicle Information: 2011 GMC Sierra 3500 HD Denali 6.6L

Issue + Repair History: The truck initially had a P0708 code for transmission range switch voltage high (MLPS issue). Over time, it started registering random codes that would appear and disappear, leaving only the P0708 and P0894 codes (trans component slipping without the truck moving). The following actions were taken:

• Replaced the MLPS (Neutral Safety Switch)
• Replaced the internal harness
• Serviced the transmission (fluid and both filters)
• Replaced the TCM (Transmission Control Module) with a preprogrammed unit from NPC in Texas

However, the problem persisted, especially when the engine bay got hot. The new TCM exhibited similar behavior, logging multiple codes randomly.

Other OBD2 Codes + Test Results: A total of 44 codes were logged randomly, including P0708 and P0701 (transmission range switch circuit performance), but they would come and go without a clear reason.

Suggestions to Fix Issue:

1. Check for Interference: Investigate the possibility of interference from another source affecting the TCM.
2. Inspect Serpentine Belt: Check if there is an aftermarket serpentine belt on the truck, as it may cause static discharge issues.
3. Relocate TCM: Consider relocating the TCM as per TSB instructions to mitigate potential EMI or RFI.
4. Add Clamping Diode: If there’s any solenoid-operated electrical equipment, add a clamping diode to prevent voltage spikes from damaging the TCM.

Final Fix: The issue was resolved by replacing the TCM with a new GM unit and programming it. The original and the replacement TCMs exhibited issues when their temperature reached approximately 85 degrees Fahrenheit. It was determined that the TCM was faulty, and a new GM unit fixed the problem.

Case #4: Mercedes

Vehicle Information:

• Year: 2009
• Make: Mercedes-Benz
• Model: E350
• Engine: 3.5L

Issue + Repair History: The vehicle experienced jerky shifting and occasionally went into limp mode. Restarting the car temporarily resolved the issue. No faults related to the conductor plate were found. The problem was suspected to be related to the bolts holding the reverse drum.

Additional faults were found on the Electronic Selector Module (ESM):

• P1861: The rear left wheel speed signal sent from the traction system via the CAN bus is implausible.
• P1860: The rear right wheel speed signal sent from the traction system via the CAN Bus is implausible.

Other OBD2 Codes + Test Results: The following fault codes were also present:

• P0894: The gear is implausible or the transmission is slipping.
• P0734: The gear is implausible or the transmission is slipping (Gear 4).
• P0735: The gear is implausible or the transmission is slipping (Gear 4).
• P0893: Hydraulic fault in the transmission.

Final Fix:

1. Replaced the selector plate.
2. Inspected solenoids (found 2 clogged and 1 seal gone).
3. Swapped solenoids from another transmission.
4. Dropped the transmission and found damaged K1 clutches.
5. Replaced the transmission with another unit, transferred the selector plate and valve body.
6. Reflashed the new transmission, cleared codes, and performed adaptations.
7. The vehicle was then working as designed.

It was a challenging diagnosis, but the replacement of the transmission ultimately resolved the issue.

Case #5: Chevrolet

Vehicle Information:

• Year: 2004
• Make: Chevrolet
• Model: Trailblazer LS
• Engine: 4.2L

Issue + Repair History: The vehicle initially came in with a perceived slipping condition. The transmission was overhauled, and the following TSBs were followed:

• 01-07-30-038D for the slipping issue.
• 08-07-30-008B for the TCC (Torque Converter Clutch) issue.

However, the TCC was still not engaging when commanded. Despite replacing all solenoids and the wiring harness during the overhaul, the problem persisted. Other parts replaced included gaskets, seals, torque converter, bushing kit, band, filter, reaction shell, forward sprag, input drum with shaft, and sealing rings on the input shaft and pump stator.

After reassembling the unit and replacing the entire valve body, the problem remained. The PWM valve was also blocked off to provide full TCC engagement when commanded. Despite extensive troubleshooting, the TCC was not engaging, and the P0894 code continued to be set.

Other OBD2 Codes + Test Results: In addition to P0894, the following fault codes were present:

• P0757: Shift Solenoid ‘B’ Stuck On.
• P0893: Hydraulic fault in transmission.

Final Fix: After multiple attempts to diagnose and repair the TCC issue, the decision was made to purchase a rebuilt ETE unit, which was installed, resolving the problem.

While the issue was resolved with a replacement transmission, the exact cause of the TCC problem was not identified during the troubleshooting process. Multiple components were replaced in an attempt to fix the issue, but it persisted until the replacement transmission was installed.

Advice	Diagnostic Step Description
Check for correct fluid level and quality	Ensure the transmission fluid level is correct and in good condition.
Inspect the TCC apply valve in the pump	Examine the TCC apply valve in the transmission pump for proper function and orientation.
Check the TCC solenoid and wiring	Verify the condition of the TCC solenoid and its wiring harness.
Inspect the valve body for wear and issues	Examine the valve body for wear, especially the TCC bore, which can affect TCC function.
Verify cooler flow through the transmission cooler	Ensure that there is proper fluid flow through the transmission cooler to prevent overheating.
Perform an air check of the fluid circuits with solenoids on and off	Check fluid circuit operation by performing an air check with TCC solenoids on and off.
Consider replacing the torque converter if other checks fail	If all other diagnostic steps fail to resolve the issue, consider replacing the torque converter.