Written by Jim Stokes – Warranty Technician
Jim has held many titles in his 12 years at Certified Transmission. He’s been a service writer, diagnostician, helped run Certified shops, and has now been a part of the warranty team for almost 10 years.
Our company sells hundreds of wholesale carry-out units, as well as performing thousands of in-house installations. Our talented team of technical advisers provides guidance for both types of installs, and we’ve found a number of common issues that installers face on a daily basis. In Part 2 of this series, we will be exploring the remaining 6 top install problems we encounter.
5. Power and Grounds
The GM trucks with 4L60E and 4L80E transmissions seem to frequently have power supply issues. Defective ignition switches are the normal cause of the problem, and we have seen a few vehicles with aftermarket products incorrectly wired into the power supply circuit for the transmission. We suspect that many transmissions have been misdiagnosed and sold for symptoms created by the bad ignition switches, as we have had several calls immediately after install reporting a concern identical to the unit that was just replaced. GM TSB 01-07-30-002A goes back to 1997, but we have seen the problem in 1994 models. The TSB has been updated to 01-07-30-002E to 2005 models, so it affects a lot of vehicles on the road today.
We have had several calls on Toyota vehicles that won’t start, won’t shift, and wrong gear starts right after installation of a replacement transmission. A poor ground connection at the transmission case is often the cause, and sometimes at the battery ground also. We have seen similar concerns in other vehicle makes, also. The most prone vehicles are power-side controlled systems, where the PCM/TCM sends voltage to the solenoid being controlled and the solenoids are permanently grounded to the valve body. With this type of control system, ground cables are connected directly to the transmission case. These ground cable connections are often used for PCM/TCM return signals, so they must be clean and secure.
All power and ground connections must be clean and free of excessive resistance. Since the battery is usually disconnected when installing a unit, clean the connections before connecting them.
6. Engine Sensors
Engine sensors have a big impact on transmission performance. MAF, TPS, oxygen sensors, knock sensors, and coolant sensors are all potential trouble for the transmission’s correct operation.
We had a 2002 Buick Century with a freshly-installed, remanufactured 4T65E. It had slow, soft upshifts, and if heavy throttle was applied, it would slip. It wasn’t driven long enough to set GRE codes, but it would have set codes if driven for any amount of distance. The installer was an industry veteran at a quality shop, so I sent him a replacement unit based on his own diagnosis. After installing the replacement unit, it had the same problems as the unit just removed. He installed a pressure gauge and found that the unit had no line rise with increased engine load. He connected a scanner and manually controlled the PC solenoid, and the pressures stayed in spec with each increased pressure command. After replacing the MAF sensor, the unit worked as designed. The engine did not have any drivability concerns, and no DTC’s set. Because the MAF was bad, incorrect load calculations from the PCM were causing a slip condition.
Engine coolant temperature sensors can cause 518/618 units to go in and out of lock-up if they fluctuate around 160 degrees, where TCC engagement is allowed on. The same vehicles can have a no upshift complaint, or incorrect gear starts if the oxygen sensor ground is lost or contaminated. The governor solenoid and the O2 sensors share grounds.
We recently had a 2000 Lexus RX300 that didn’t have 4th gear immediately after install. After hours of unsuccessful diagnosis, it was discovered that the exhaust manifold was leaking near a knock sensor, and caused the PCM to inhibit the shift. These same vehicles will not shift to 4th gear if a knock sensor code is present.
Improper TPS signals will affect multiple vehicles causing them to have soft or harsh upshifts, engagements, early shifts, slipping lock-up clutches, and shuddering.
7. Performance modifications
Applying modifications that result in a large increase to engine performance, but without modifying the transmission, is nearly always going to end up badly. The easily-added performance chip, download, or module can add up to 100 or more HP and torque to an engine, but the factory has the original programming tuned to protect the OE transmission from damage. When that protection is removed, it usually ends badly for a stock-level transmission, but if the repairs are done correctly with the knowledge of the modification, it can be very profitable. Be careful of these vehicles because without that knowledge it can be a costly mistake for the repair shop.
8. Converter bolts
Proper installation and usage of converter bolts is critical to avoiding a major failure. We have had units returned with converter dimpling problems from 4L60E units, all Chrysler units, Toyota units, KM models, and most recently a rash of AW55-51SN units in both Nissan and Volvo applications. Just the slightest dimple in the converter cover will eventually cause a clutch failure to occur. We have seen it happen anywhere from 10 to 7000 miles of use and the end results are always the same. Verify that the correct, OE-spec bolts are used in all mounting holes since it only takes one incorrect bolt to cause failure. Also, use a torque wrench when tightening the converter bolts.
A remanufactured or rebuilt unit is going to have all new seals installed, preferably with the best quality available. All seals should be installed with alignment tools that keep them straight and in alignment, and if it is a metal-clad seal the metal portion should be sealed to the case and the proper tool that sets them to the correct depth. A word of caution: inspect yokes and axles carefully for damage and wear before installing them, and be careful not to bang into them when installing a unit.
10. Cooler cleaning and contamination
Proper cooler cleaning is a problem for the remanufacturing industry. Not so much with professional transmission shop installations, but more so with the general repair shops that do not have access to the proper equipment needed for modern vehicle cooler flushing.
Another problem we see often is fluid contamination originating from dirty coolers, and intrusion through the vents. Ford has issued TSB 05-23-7 for 1999-2003 Windstar, and 2004-2006 Freestar vehicles for water getting into the units through the vent. Water is routed from the cowl under the windshield and ends up in the transmission vent. The cowl requires modification to correct the condition, and I would also suggest adding a hose to the vent to relocate it and have it face downward, if possible. We have seen many units damaged from water intrusion both in cores, and returned failed units.