As the rebuild technician removes the solenoids from the valve body, a rubber gasket falls on the bench. The technician did not see where this gasket came from and therefore does not know where it goes.
The technician did not have knowledge of the gasket’s existence and was not expecting it to appear.
The rubber gasket is installed under the front-brake-band solenoid connector (Figure 1).
The location of the gasket is shown in Figure 2.
None of the other solenoids has a gasket under it. One reason the gasket is placed where it is may be because the front-brake-band solenoid is on in every gear except fourth. Because it spends so much time on, it may be that oil could find its way past the solenoid connector and into the TCM.
A 2004 Nissan Armada or Titan may come into the shop with the MIL illuminated and code P1774 for the low/coast-brake-solenoid function is retrieved. The technician may also retrieve code P1730 for transmission interlock (not shiftlock) fault or P1731 for first-gear engine-braking fault.
Incorrect TCM programming.
Reprogram the TCM based on the part number of the TCM found in the vehicle and compare it with the TCM part numbers in the chart in Figure 3. If the TCM part number is not in the chart, proceed with diagnostics to locate the cause of the faults.
Reflash the TCM as per TSB AT04-010
2004-up Subaru models equipped with the 4AT or 5AT transmission may exhibit a complaint of a 2-3 upshift flare and/or harsh downshifts after overhaul.
The cause may be that the transmission adaptives were not reset after overhaul.
To correct this condition, the vehicle will need to be reset with a factory scan tool. Subaru TSB #16-72-07 explains how to perform the A/T learning control procedure with the SSMlll scan tool. This learn control must be performed when the TCM is reprogrammed, the transmission has been overhauled or the valve body has been replaced. The adaptives cannot be reset by driving the vehicle and must be reset with the factory scan tool. See Figure 4 for a list of vehicles that require the A/T learning control procedure.
A 2001-2003 RAV4 may come into the shop exhibiting improper transmission operation such as a 2-3 bind-up, harsh shifts, direct-clutch failure or storage of shift-solenoid A or B electrical or performance codes.
A defective powertrain control module and/or compromised TCM ground circuits.
Provide good grounds for the TCM first. If the problem persists, replace the TCM.
Originally Toyota would warrant the PCM under emissions coverage for 80,000 miles or 96 months, whichever came first.
Via a letter to the dealers from the manufacturer (no bulletin), this warranty has now been extended to 150,000 miles or 10 years from the vehicle’s “in-service” date.
The warranty enhancement stipulates that once the Toyota dealer verifies the cause of the complaint, the PCM and/or the transaxle will be replaced at no charge.
In some instances a mechanical problem exists with the transmission but a code for this problem stores intermittently. When the vehicle is brought to the shop and scanned for codes there may be none even though the vehicle exhibits symptoms.
Toyota uses two-trip logic for code detection. Therefore, it may take two or more days for the code criteria to be met and the code is stored.
Using a capable scan tool put the ECM into “check mode” (Figure 5), which will allow the code to set after one trip; the vehicle will have to be driven for a short while. These codes can be TCC slip such as P0770, solenoid performance such as P0756 or a gear-ratio error such as P0734. Once the code is retrieved be sure to take the ECM out of check mode, using the scan tool to do so.
There are two reasons for stored codes to be erased:
- One is if the scan tool is used to switch from normal mode to check mode or vice-versa.
- Two is that in check mode the ignition is turned to the ACC or LOCK position; therefore, it would be a good practice to record any codes that may exist.
The transmission works fine cold but goes to default intermittently when warm or goes to default regularly when warm with one or more speed-sensor codes before and/or after rebuild.
One cause may be a bad connection where the internal harness connects to the pigtail lead of each of the sensors (figures 6 & 7).
The input-speed-sensor connector is white and the output-speed-sensor connector is blue (Figure 8).
These connectors snap onto a metal bracket, securing them in place. In time, with heat, these connectors get brittle and can easily break the lock/snap feature of the connector during removal of the valve body. When they’re reconnected, a compromised connection may cause intermittent setting of codes.
Another cause can be that the sensor itself has failed or is defective or cracked. A technician may overlook this by thinking that the temperature-related condition for setting the code eliminates the sensor as a possibility. The ISS and the OSS are Hall-effect sensors and can operate well when cold but fail when hot. Depending on the failure, an internal short or open can easily occur with temperature.
A resistance check of the ISS or OSS may discover a problem when there is a permanent hard open or a short in the sensor. For example, in figures 6 and 7 the ISS and OSS measure 5 megohms each. If you had 1 ohm you discovered a short. If you had nothing, either it’s open or your meter is not set properly. However, because of the design of Hall-effect sensors it is best to check them with an oscilloscope, especially when there is an intermittent sensor problem.
Both the ISS and OSS receive approximate system voltage and send back to the computer a 1-volt pulse from an approximate 0.5 volt to 1.5 volts DC (Figure 9).
A two-channel scope could check one sensor at a time; a four-channel scope could check both simultaneously.
Figure 9 provides an example of good sensor signals. Both the ISS and the OSS maintain a steady voltage supply (channels 1 & 3) and the signal patterns are clean 1-volt pulses with a pulse count that increases and decreases with speed (channels 2 & 4). A close look at the signal also reveals a solid 1-volt pulse from an approximate 0.5 volt to 1.5 volts DC.
If there is a signal drop-out, check connections and repair accordingly. If the power supply remains steady yet the signal suddenly drops out, replace the sensor.
Note: Most Aisin transmissions’ ISS and OSS signals are checked in this fashion.
Before and after rebuild the transmission may experience intermittent flared or harsh shifts when warm.
Defective solenoids, valve-body bore wear, compromised counterbalance molded pistons, bushing wear, excessive endplay and a loss of internal-transmission-cooler pressures are some of the more-common reasons for this type of complaint, not to mention the need to reset shift adapts. Another possible cause that often goes unnoticed is a malfunctioning transmission-fluid-temperature sensor (Figure 10).
This sensor influences line pressure and may cause line pressure to act irrationally. Also, the O-ring (Figure 11) must seal, as the sensor is situated directly in the main line-pressure circuit next to the pressure-regulator valve. If the O-ring leaks, a stream of oil will pass by the O-ring and possibly cause aeration of the fluid, also resulting in line-pressure instability.
Repair or replace as necessary. Figure 12 provides a resistance-check chart.
November 2012 Issue
Volume 29, No. 11
- Nissan RE5R05A: Solenoid gasket
- Nissan RE5R05A: False code P1774
- 2004-up Subaru 4AT and 5AT: 2-3 flare and/or harsh downshifts
- 2001-03 Toyota RAV4: PCM warranty enhancements
- Toyota: ECM check mode
- TF60-SN, 09G, 09K, 09M: ISS-OSS codes
- TF60-SN, 09G, 09K, 09M: Flared or harsh shifts