Automatic Transmission Pressure Testing

[@sivucit]

Hi, you become my bible when it comes to Transmission questions. 1. When will you do line pressure test ?.. lets say i have delayed shifting on 2nd gear, and say there are 2 scenarios. a. line pressure shift fail. b. line pressure shift pass. what would you transmission specialist would do for above scenario. how this test will help him to take it for next steps. I am bit confused about next steps of pressure test.. and is this still valid in CVT as well.

[@sivucit]

Hi, I have 2005 pilot today i changed 4th cluth pressure sensor. Question is, what is the purpose of this, ?.. i understand shift solenoid is responsible for opening up passage in valve, i assume pressure sensor is feedback to ECM/TCM to let it know that shift solenoid is working fine based on pressure build up .. please advise. 2) question is how do i know the car is in 1,2,3,4 gear, i used scan tool and look at solenoid a,bc, etc. i assume based on on and off condition on various solenoid we know what gear it is, not sure why scan tool just dpont let us know what gear car is going based on various on / off .. is there a way while driving we can find out what gear it goes based on rpm shifting down..

[@DrivelineMaster]

Clutch pressure sensors typically provide feedback to: 1) confirm proper pressure build up for the clutch pack to verify the pressure in the circuit. This is also used with the input shaft speed sensor and the output shaft speed sensor to verify the gear ratio (shift) occurred. 2) they can provide feedback on how long it took to completely fill the clutch or reach a specified pressure. This information is typically used to provide adaptive controls. For example if 60 PSI is sent to a clutch and the computer expects the sensor to read 60 PSI between .25 seconds and 1.25 seconds after the shift solenoid switches but the sensor reports that it took 1.5 seconds the computer can modify the signal to the shift solenoid so 65 PSI is now sent to the clutch pack in an effort to get the pressure sensor to report that the shift is now within .25 and 1.25 seconds. This is adaptive controls and it improves shift quality and transmission life over the life of the transmission. Question 2, Most but not all scan tools and transmission or powertrain control modules will have a gear PID (Parameter ID) This will tell you what gear your in. If you don't have that info it could be one of two possibilities. Either the control module can not provide that to the scan tool or the scan tool is unable to retrieve it from the module. The only other way is to feel the shift and watch the tachometer. If you can monitor the shift solenoids you might be able to map out the sequence for each gear if they are simple on/off solenoids. Sometimes the shift solenoid map is available in the service manual but not for most Honda's. Honda's don't typically have simple on/off solenoids for shift but instead they use Pulse Width Modulated (PWM) solenoids they call Clutch Pressure Control (CPC) solenoids. These are difficult to determine when they are activated for each shift. The value on a scan tool is normally in amperage. OK, I just looked it up. You do have CPC and on/off solenoids. N to D1 (SSA=Off, SSB=on, SSC=Off), D1 driving all solenoids are on, D2 driving (SSA = On, SSB = On, SSC=Off) D3 driving (SSA=Off, SSB=On, SSC=On) D4 driving all solenoids are Off, D5 driving (SSA=On, SSB=Off, SSC=On. Hope this helps.

[@sivucit]

@@DrivelineMaster Thanks so much . Appreciate your detail write up. One last question, Toyota have all solenoid and clutch pressure sensor inside the transmission attached to valve body, howeer honda have it outside the transmissoin which makes easy to change. Do you know why honda made this way then Toyota

[@DrivelineMaster]

Honda is the oddball. Almost all other manufactures put the solenoids inside on the valve body. It all has to do with the design of the transmission. Honda and Acura use an auto trans that uses helical gears similar to a manual transmission where most others (excluding CVT and DTC transmissions) use planetary gears.

[@sivucit]

@@DrivelineMaster Thanks again, 2 Questions . 1. When a solenoid / pressure sensor goes bad does that always come with an error coe in TCM or ECM. 2. When a trans is rebuild is it mandatory to change valve body with reman / OEM one bcz i was told testing valve body is not that easy and when doing trans repair it is practice to have a reman valve body installed.

[@DrivelineMaster]

Different shops have different practices and capabilities. Some shops have the tools, skills and time to perform comprehensive tests and repairs to a valve body and some don't. Some just don't want to bother with the complexity or disassemble, clean and inspection. To be on the safe side a lot of shops will always recommend to replace the valve body with a reconditioned one. Reconditioned VB are almost always tested with specialized testing equipment to ensure they are working properly and it is good insurance for the rebuild shop to ensure customer satisfaction to install a quality rebuilt VB so I would not fault them for doing this. Sensors and solenoids have extreme failures. the circuit is open or shorted and these will always set a code. What is more unusual are solenoids or sensors that function but not always within the proper perimeters and these can be difficult to diagnose because they may not set a code but they will cause symptoms. Computers are designed and set a code when an electrical component is operating outside of the designed range however, if the component is within range but inaccurate such as a pressure sensor reading 25 PSI when the actual is 10 PSI and the sensor range of operation is between 0 and 60 PSI this is a problem. This may not set a code but it will cause a problem with the proper operation of the transmission.

[@Fabian080690]

how much does a shop could charge for this procedure for testing a used prospect car I'm looking to buy?

[@DrivelineMaster]

Each vehicle is different where some are easier to do than others. This is not a normal pre-purchase test. Have a shop perform a pre-purchase inspection and road test. A good mechanic should be able to tell if the transmission has problems based on the road test and the fluid condition.

[@mustafaalsaadi6757]

Hi sir I have a 097 Audi80 B4 gearbox The problem is harsh 3rd gear I tried alot of experiments to solve it but nothing is working Finally we delt with the pressure selinoid I fixed the current to that selinoid (N93) to 0.9 amp and gave a test drive Everything was good but as far I know the current I fixed keeps the selinoid shunt! So I think I increased the pressure in valve body! any suggestions? To solve the rough shift? Thanks in advance..

[@DrivelineMaster]

Finding a way to fix your pressure control solenoid at .9A is a bad idea and a good way to burn up the clutch packs in your transmission. You lowered the pressure in the entire system and when your clutch packs need more pressure for heavy load driving conditions the pressure won't be there and the clutch pack will slip and burn up. Each transmission has specific ways for softening the shift and they often will combine multiple techniques such as combining a check ball and orifice along with an accumulator. Newer vehicles will use Pulse Width Modulated (PWM) solenoids to control the shift valve opening. There may be a technical service bulletin on this problem. If I find some time I will look and see if I can provide some specific answers for you. In the meantime remove what ever you have done to cause the pressure control solenoid current to be fixed at .9A.

[@tpicaro]

Thank You