Issue Summary:
- A 4T80-E may exhibit suddenly firm shifts accompanies by intermittent ratio codes P0731 and P0732.
- After a valve-body exchange during either a rebuild or a repair, an AX4S/AXODE exhibits a harsh upshift into 2nd gear. No codes are present, and a pressure check verifies that line pressure is within specifications.
- A new drain-plug transmission kit is available to prevent leaks from the oil-pan plug on Toyota models.
The vehicle may suddenly exhibit firm shifts. This may be accompanied by the illumination of the malfunction indicator light or a “Service Transmission” displayed in Cadillac’s Driver Information Center. When the vehicle is scanned for codes, a first-gear-ratio error P0731 and/or second-gear-ratio error P0732 is stored in the PCM’s failure and history records.
Besides the typical possibilities such as low fluid level, restricted filter, a compromised forward-clutch circuit, forward sprag, low/reverse-band circuit, 2nd clutch, 2nd sprag, stuck or sticking shift valves or mechanically failed solenoids, another possibility that needs to be considered is a faulty transmission-fluid-pressure (TFP) sensor (see Figure 1).
Should the TFP sensor suddenly indicate an erroneous Park/Neutral position signal to the PCM during heavy throttle demands, the PCM will initiate a torque-abuse protection strategy. This strategy will manage engine torque, resulting in a decreased input-speed signal from the transmission altering gear-ratio calculation beyond the acceptable tolerances, which will produce these false gear-ratio error codes.
As a result of the PCM’s employing the torque-abuse strategy, you may observe a loss of power during heavy-throttle acceleration, providing a tip that the TFP sensor may be the culprit.
Fortunately, the TFP sensor is accessible from the bottom pan, as it is attached to the lower control-valve assembly as previously seen in Figure 1, making its replacement an easy task. You can monitor this sensor via a scan tool or through the Driver Information Center to ensure that its replacement will solve the problem.
Clear codes, and drive the vehicle with the selector lever in the D4 position. The pressure-sensor status should always indicate this D4 position to the PCM. Observe this reading under various throttle demands, especially under heavy-throttle conditions. If the sensor changes state, the sensor assembly and/or wiring should be repaired or replaced.
After a valve-body exchange during either a rebuild or a repair, the vehicle exhibits a harsh upshift into 2nd gear. No codes are present, and a pressure check verifies that line pressure is within specifications.
One cause may be that an incorrect valve body was used. The converter-clutch regulator-valve line-up was revised in 1996. Figure 2 shows the configuration of the TCC regulator valve for the 1991-95 model years; Figure 3 shows the configuration for 1996 and up models.
Install the correct valve body with its own spacer plate, as the hole configuration matches the valve body.
All 1996 to 2000 Rodeos (UE), Amigos (UA) and Troopers (UX) and 1999 to 2000 VehiCROSS (VX) V-6 models with transmission serial numbers starting at 4754596 and going to 5831756 are experiencing an oil-plug leak in the main pan of the transmission. The main pan has both a drain plug and an overfill plug, and either or both could be leaking (see Figure 4).
Improper surface finish on the oil pan.
A new drain-plug transmission kit available under Isuzu part No. 8-96041-810-0 eliminates this leaking condition. There is one plug per part number, and it can be used in either location. If both are leaking you will need to order two of this part.
Special Note:
Do not open the overfill plug with the engine off, as the level does rise past the overfill plug from typical drainage.
Following proper repair procedures is imperative when you are working on a hybrid electric vehicle (HEV), as these vehicles have several sources of high voltage. These high-voltage sources must be neutralized for the same reason you must turn off the circuit breaker in your house before you work on the electric water heater. In other words, if you do not power down the system correctly, you may experience a hazardous shock. The main items to be concerned with in a typical hybrid electric vehicle are the battery system, the motor/generator and the condenser.
The Battery System:
The battery system is made safe by removing a service plug that interrupts the circuit between the two battery packs.
The Motor/Generator:
The motor/generator in an HEV is a permanent-magnet type. It does not need any “excitation” or “field” voltage to generate electricity or mechanical force. Anytime this motor/generator is turned, it WILL generate electricity. Removing the service plug interrupting the battery circuit does not prevent the motor/generator from producing voltage in the system if it is turned. This is why you must take great care when doing anything that will cause the motor/generator to turn, such as pushing the car or turning a tire by hand.
The Condenser:
Anytime you put loads on electric motors and electric generators, there is a spike until the load settles. To combat this problem the HEV uses large condensers. These condensers will hold a charge for several minutes. This is why you must wait five minutes after removing the service plug before attempting any repairs. In the Toyota Prius the condensers are in the motor-driver module in the engine compartment.
High-Voltage Wiring:
High-voltage wiring in all HEVs is orange. It may have orange high-voltage insulation like that on high-performance spark-plug wires, may have orange tape wrapped around it or may be in orange wire-loom material. Even after you have followed all the proper procedures, it is most strongly recommended that you always avoid all orange wires.
High-Voltage Batteries:
The high-voltage batteries contain a strong alkaline electrolyte. ANY leakage from the battery module is serious. You can use a solution of boric acid to neutralize the corrosive effects of leaking potassium-hydroxide electrolyte until a permanent repair (battery-pack replacement) can be made. Do NOT allow the electrolyte to touch your skin.
Figure 5 shows the service plug that needs to be removed before any type of repair begins with a 2001 1.5-liter Toyota Prius. Because of the discharge resistance, it will take 5 minutes before the 273.6-volt electricity is sufficiently discharged from the condenser to the inverter circuit after removal of the service plug. The partial wiring diagram provided shows the orange wires as they go from the batteries in the trunk to the inverter, which is in the front engine compartment.
The transaxle experiences delayed engagements of more than three seconds under different temperature conditions. This excludes any delayed-engagement complaints on startup after the vehicle has been parked for several days, as this is to be considered normal.
The variety of possibilities follows:
- Low fluid level
- Restricted filter or malfunctioning filter and/or filter O-ring
- Pressure regulator valve stuck or sticking
- Malfunctioning pump
- Leaks in the low/reverse-clutch circuit
- Operational problems with the low/reverse #1 checkball in the valve body
- Underdrive-clutch circuit leaks
- Malfunction of PRNDL switch or switch circuit
- Electrical noise in the OSS circuit
Low fluid level, filter concerns, or problems with the pressure regulator or pump may be accompanied by pressure-switch codes and/or code 35, loss of pump prime. The first step is to observe the fluid level on the stick before starting the vehicle and then observe the level with the vehicle running. The fluid level before you start the vehicle should be above the full mark. Once the vehicle has been started, the level should drop to the full mark.
If the fluid is low, you will need to fill the transmission to the full mark and check to see whether this resolves the complaint. If it does, you will need to identify and repair the leak causing the low fluid level.
However, if the level didn’t drop to the full mark quickly or at all, the filter may be restricted and will need to be investigated. If the filter is restricted, the material restricting the filter will determine the next logical repair procedure.
If the fluid level seems to have risen, the pump may be drawing air as a result of an incorrectly installed filter or the O-ring is not sealing, and you will need to investigate and correct the problem.
The pump also may be part of the problem. You usually can detect foaming of the fluid the moment you remove the dipstick, confirming a cavitation concern. As noted in the July issue of Transmission Tech/Talk, a bypass valve stuck in the open position also will produce a high, foamy fluid level.
If the fluid level is correct and delayed engagements persist, the pressure regulator could be stuck or sticking. You can verify this by checking it either physically or with a pressure gauge. A physical check would be to pull the valve body down and remove and clean the pressure-regulator valve to ensure proper operation. To check it with a pressure gauge, attach the gauge to both the low/reverse and underdrive pressure taps (see Figure 6). In drive with the brake applied and engine speed brought up to 1,000 rpm, both circuits should show about 120 psi. If both are the same but significantly low, the pressure-regulator valve and/or pump needs to be repaired or replaced.
If just the low/reverse pressure is down, the low/reverse-clutch circuit has a leak and will need to be repaired. This could mean a problem with the accumulator-piston seals, the low/reverse-piston seals, or dog dish and gasket. This type of failure may be accompanied by codes 36, 50 and/or 51 and produce a slow-down pump complaint.
One other possibility regarding the low/reverse-clutch circuit is the #1 shuttle ball in the valve body (see Figure 7). If there is insufficient clearance for the ball to roll when the unit gets hot, the ball can stick or drag against the spacer plate and cause a delayed application of the low/reverse clutch. The minimum acceptable clearance from the top of the ball to the surface of the valve body given by the manufacturer is 0.007 inch. About 0.040 inch is typical, but some valve-body castings have been known to have too shallow a bathtub pocket so that the ball is pinched against the plate when the transmission is hot.
This ball has been eliminated and replaced with a low/reverse-switch valve (see Figure 8). This new-style valve body is available for units either with or without a transmission-range switch.
If just the underdrive pressure is low, the under-drive-clutch circuit has a leak and will need to be repaired. This could mean a problem with the accumulator-piston seals and/or the underdrive-piston seals and O-rings. This type of failure may be accompanied by codes 36 and 51 and may produce a delay from neutral to OD when the transmission is cold.
When the PRNODL switch causes delays in Drive and Reverse, many times it is intermittent and produces a code 24. The switch can stick or freeze, sending erroneous or erratic signals to the TCM, which makes it difficult to detect with a scan tool unless it is so bad that the problem is consistent enough to be caught on data stream. If the PRN-ODL switch is questionable, change the switch.
Enough electrical noise in the output-shaft-speed (OSS) sensor could initiate the reverse-block-out feature in the TCM. 1996 and later TRS-style units have incorporated a temperature sensor into the switch. This sensor shares a ground at the TCM with the TSS and OSS, and that is terminal 13 (the OSS uses terminals 13 and 14, and the TSS uses 13 and 52 at the TCM). With the vehicle idling in Park, the OSS should read 0 rpm. If output speed should exceed 400 rpm, the reverse-block-out feature will be initiated. If noise is present, you will need to investigate each wire to determine the source of the noise and eliminate it.
Tip:
The source could be an ignition wire running close to the speed-sensor wires.
August 2002 Issue
Volume 19, No. 8
- 4T80-E: Intermittent Ratio Codes P0731 and P0732
- AX4S/AXODE: Harsh 1-2 Upshift
- 4L30-E: Leak From Oil-Pan Plug
- Toyota Hybrid: Electrical Service Precaution
- 41TE and 42LE: Delayed Engagements