Issue Summary:
- After an overhaul during which the channel plate is replaced, a THM 4T40-E may have various stuck valves caused by mysterious metal particles.
- Before and/or after rebuild of a THM 4T40-E, the vehicle illuminates the check engine lamp and stores code P1887 or P0742 in memory.
- After overhaul and replacement of the torque converter in a THM 4T60-E, code P1870 – transaxle component slipping – occurs during the road test.
- In a THM 4T60-E, an incorrect pressure switch or one that is stuck closed can cause no or a late 1-2 shift or cause the unit to fall back to third gear after attempting a 3-4 shift.
- Some 1995-96 Buick Century and Oldsmobile Ciera vehicles with the 3.1-liter engine and THM 4T60-E may exhibit 3rd-gear starts and the air conditioner not working because of a blown in-line fuse.
The transmission has been overhauled, and during the inspection it was determined that the channel plate needed replacement. The transmission now exhibits various problems, and the diagnostic procedure seems to lead to the valve body. When the valve body is inspected, various valves are found to be stuck. What may happen next is that the valves are freed and the transmission is reassembled, only to have this complaint repeat itself.
New channel plates DO NOT have threads (see Figure 1) cut into the holes for the bolts that fasten the valve body to the channel plate. Bolts with self-tapping threads are used and cut threads into the bolt holes as they are screwed into the channel plate. If this is done with the channel plate bolted to the case, the metal shavings generated by the bolts cutting into the channel plate produce the “mystery metal” that causes the valves to stick.
Cut threads into the bolt holes before installing the channel plate onto the case.
- 1995-96 Channel Plate. . . . . . . . . . . . . . . 24213174
- 1997-01 Channel Plate. . . . . . . . . . . . . . . 24213193
Before and/or after rebuild, the vehicle illuminates the Check Engine lamp and stores code P1887 or P0742 in memory. Once the code is stored, TCC will be inhibited and maximum line pressure will be set, creating harsh engagements and shifts.
P1887 Code Definition: TCC Release Switch Circuit Malfunction.
P0742 Code Definition: TCC Locked On.
This is usually created by a leak of TCC release oil through the needle-bearing and seal assembly in the oil pump (see Figure 2).
This needle-bearing and seal assembly is now available under Transtar part number 67922B, which is a 2000 and later AX4N pump-bearing and seal assembly. The AX4N bearing is not available from Ford Motor Co. The bearing is also available from Sonnax® under part number 33000-01. In some instances, because of the bearing failure, the entire pump assembly will have to be replaced and is available under OEM part number 24208987.
This needle-bearing and seal assembly has been such a high-failure item that ATSG recommends replacing it on every rebuild.
- Needle-bearing and seal assembly (Transtar number) . . . . . . .67922B
- Needle-bearing and seal assembly (Sonnax number) …….. 33000-01
- Oil-pump assembly complete . . . . . . . . .24208987
The transmission has been overhauled and the torque converter has been replaced. The TCC regulator valve also has been addressed, but during the road test code P1870 is stored, which was the original complaint. When data is read on the scan tool, TCC duty cycle is at maximum, yet the TCC slip cannot be brought within specifications.
1. The TCC apply valve behind the TCC enable solenoid was not inspected for wear. It is not uncommon for this valve to wear, causing converter-clutch slippage or falling out of lockup when the transmission is hot.
2. Sonnax has available a TCC-apply-valve repair kit (see Figure 3). The kit contains a Teflon® sealing ring to compensate for the wear that occurs in the area of the outermost spool of the valve. There are two standard-size valves, one for 1991-96 and one for 1997 and later units.
The outermost spools of these valves are dimensionally different (see figures 4 and 5). This complaint occurs when the 1991-96 valve is mistakenly installed in a 1997 or later valve body.
Figures 4 and 5 show the dimensions for both the late and early standard valves. Another means of identification is valve material: The 1991-96 valves are steel for both original equipment and the Sonnax replacement. The 1997 and later valves are aluminum for both original equipment and the Sonnax replacement.
If there is wear on the inner spools as well, Sonnax has available oversize valves for 1991-96 and 1997 and later. Figures 6 and 7 show the dimensions for the late and early oversize valves. As with the standard valves, the 1991-96 original-equipment valve and the Sonnax replacement valve are steel and the 1997 and later valves are aluminum. The oversize valves will require a drill jig and a reamer, also available from Sonnax.
- Be sure to check both the TCC apply valve and the TCC regulator valve for wear. If wear is present, use the appropriate Sonnax valve-repair kit.
- Use the dimensionally correct valve kit for the model-year transaxle being repaired.
- 1991-96 TCC apply valve, standardsize . . . . . . . . . . . . . . . . . . .84754-22K
- 1997 & later TCC apply valve, standard size . . . . . . . . . . . . . . . .84754-98K
- 1991-96 TCC apply valve, oversize . . . . . . . . . . . . . . . . . . . . . . . .84754-16K
- 1997 & later TCC apply valve, oversize . . . . . . . . . . . . . . . . . . .84754-97K
- Drill jig only . . . . . . . . . . . . . . . . . . . . . . .84754-DJ2
- Reamer and drill jig . . . . . . . . . . . . . . . . . .84754-TL
(1) The transaxle will not shift out of first gear, or a 1-2 shift occurs extremely late.
(2) The transaxle attempts to shift to fourth gear but immediately falls back to third gear, at which time the TCC signal is also lost.
(1) The “Lo Discrete Switch” on the oil-pump body (see Figure 8) is a normally open (N.O.) pressure switch that is closed by fluid pressure from the 1-2 shift valve when the transaxle is in manual low. This prevents an upshift when the transaxle is in manual low. When this switch is stuck closed or a normally closed (N.C.) switch is mistakenly installed, the PCM will think the transaxle is in manual low and will cause a “no-shift” condition or an extremely late 1-2 shift only.
(2) During the overhaul process the “Lo Discrete Switch” and the “4th Clutch Discrete Switch” connectors were switched. The “4th Clutch Discrete Switch” is a normally open (N.O.) switch that closes when the transaxle shifts into fourth gear and opens when a 4-3 shift is made in order to disengage TCC. When the connectors are switched and the transaxle shifts to fourth gear, the signal sent to the PCM will cause the PCM to think manual low has been selected and will immediately cause the transaxle to fall out of fourth gear, followed by the loss of TCC engagement.
(1) Make certain these switches are normally open and that they are not stuck. They can be checked on the bench with an ohmmeter and air pressure. They can also be viewed on the scan-tool data list. When the switches are open, the scan tool will display the switch state as “P1.” When the switch closes, the scan tool will display the switch state as “P2.”
(2) Make certain each pressure-switch connector is plugged into the correct pressure switch (see Figure 8).
Some 1995-96 Buick Century and Oldsmobile Ciera vehicles, equipped with the 3.1-liter (VIN “M”) engine, may exhibit 3rd-gear starts and the air conditioner not working. Since the vehicle came into a transmission shop, you immediately check for voltage at terminal “E” at the case connector and find 0 volts. After inspecting the fuse block, you discover that there are NO blown fuses even though there is a fuse identified as A/C (see Figure 9).
The cause may be a blown in-line fuse behind the instrument panel (see Figure 10) that also controls voltage to terminal “E” at the transaxle.
Remove the glove compartment for access to the in-line fuses, which are toward the passenger side of the main fuse block and are taped in a bundle, making them hard to find. Remove some of the tape and replace the A/C fuse (see Figure 10).
Figure 11 provides a wire diagram that shows why power to the transmission is lost when this in-line fuse is blown.
March 2003 Issue
Volume 19, No. 3
- THM 4T40-E: Stuck Valves, Mystery Metal
- THM 4T40-E: Trouble Code P1887 or P0742
- THM 4T60-E: Code P1870 – Transaxle Component Slipping
- THM 4T60-E: Pressure-Switch Identification
- THM 4T60-E: 3rd-Gear Starts, No A/C, No Voltage to Transmission ‘E’ Terminal