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- February 8, 2003
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- Year, Model & Trim Level
- 1992 XLT
Diagnosing Electronically Controlled Automatic Transmissions
In the old days, transmissions never saw a single electron. They were hydraulic marvels controlled by engine vacuum, governors and throttle cables. With the A4LD, we saw inklings of electronic transmission control. (For those of us in the Ex community anyway... we always came last). In the A4LD, the OD (3-4) shift and the Torque convertor lockup were electrically commanded by the Powertrain Control Module (PCM, or Computer). Suddenly the ball game changed when it came to diagnosing what might be wrong, at least for those shifts, for everyone else many, or most, shifts were controlled by the computer....a mixed bag for diagnosticians of these magnificent contraptions. Today they are all virtually all electronically controlled.
[SOAPBOX MOMENT. I think the computer control of automobiles is the single most important improvement in the last 30 years. People say it's a conspiracy to keep the shade tree mechanic from working on his or her own vehicle but that isn't so. You just have to keep up with the times. No 60's mucsle car ever told you what system was ailing... and they got rotten mileage too. I love computers in automobiles. I find them useful and fascinating. ANd they are your FRIEND.. not your enemy... DO they sometimes make life a little tough? Yep, but work WITH them and you will save more time than you lose. OFF SOAPBOX.]
In an electronically controlled transmission, the computer might not be doing what it needs to do when it needs to, often mimicking a hydraulic or mechanical problem in the transmission, so the diagnostician often doesn't know which problem is because of the hydraulic system and which is the fault of onboard computers commands. So the first course is to separate and eliminate the possibility of bad computer commands. How? we substitute a human in place of the computer.
In the “for what it’s worth†category, this thread will deal with the way FORD wants their technicians to diagnose a FORD automatic transmission. I will show the use of their Transmission Tester, and discuss the pattern of diagnosis FORD promotes. While not many will have some or all these tools, the ideas presented and the knowledge of how it SHOULD be done might be valuable to those taking their vehicles to the dealer for help.
This thread is geared to the A4LD, 4R55 and 5R55 series of transmissions. The A4LD had little computer control, the 4R and 5R are practically ALL electronically controlled.
FORD has a basic diagnosis protocol. It is a good source of information – since the computer is controlling things, their first concern is to make sure every engine input to the computer is ok. SO you first check for Diagnostic Trouble Codes (DTC’s) on the engine and related sensors first, since many of these in turn drive the PCM commands to the transmission. Only once you are certain that the engine is trouble free do you move on to the transmission. Next you look for transmission DTC’s. Those you analyze and see if there is a direct issue you can fix. Failing that you hook up the transmission tester. What this does is allow you to disconnect the PCM from the transmission and directly command the transmission from the tester – eliminating any possible PCM issues. Then failing a fix, you work through hydraulic issues (using the Manual) and if that fails the FORD technicians had a help line to call. By then, it was/is probably rebuild time anyway – especially if all “non-trannie removal†attempts at fixing it had failed.
To start out, here is a great link about this issue – not FORD related.
http://www.babcox.com/editorial/bf/bf90222.htm
So with that under our belts, to start, here is the FORD protocol:
And here are the “tools†you need: A FORD Transmission manual, a high impedance voltmeter, a transmission pressure gauge, the Rotunda Transmission Tester with appropriate cable and overlay, and a scanner or code reader. A break out box is optional.
AS indicated, our first course of action is to scan the vehicle for Diagnostic Trouble Codes (DTC's). I have done a separate thread on scanners and code readers and I refer you there for accomplishing this task. (hint: put "Primer" in the search term)
Next step is to hook up the transmission tester itself. (FORD wants you to hook up a transmission pressure test gauge as well, but we'll omit that for what we are doing here - and there is a thread on that too). Each transmission has it's own special cable for hooking up to the tester. Locate the vehicle's own cable to the transmission and then unplug the vehicle transmission cable from the transmission and plug the tester connector in it's place. (You have now severed the umbilical, as it were) Like so:
The tester has "overlays" appropriate to the transmission you plan to test.
Here is the tester plugged into the A4LD with the A4LD overlay installed:
Notice that the overlay has 3 LED's on the top and those 3 LED's on the tester are illuminated. This means the tester is hooked up correctly. Now on the A4LD, the only things computer controlled are the TCC and the 3-4 shift solenoid. (not a lot in the scheme of things) We can test these and also test the diode in the solenoid setup. (For now accept that there is a "one way" street in the electrical system to run these solenoids ... we will test to see of the cop is doing his <ok ok, even her> job on that street).
Here we are testing the 3-4 shift solenoid resistance.... Notice the reading. Normal is 26 - 40ohms.
Similarly by pressing the button without an ohmeter hooked up, you could check the operation of the solenoid (the so called click test) and get a green light... I didn't get a picture of this so I'll post that later
Next I am going to turn to the TCC solenoid operation. (I was testing in the "bench" (as compared to "DRIVE") mode, so in esssence I am powering the solenoid and checking for any electrical issues.)
The TCC (here called the CCO - convertor clutch override - long story, all about how this circuit works, not important in this discussion) tests in the upper left quadrant of the tester. Here is the "green light" during the "click test".
Here is the resistance test for the same solenoid... again looking for 26 - 40 so this is a good pass.
The diode is tested by making a jumpered connection on the tester. Here I am testing the Diode (notice the LED is green - a pass- the one way street traffic cop is on duty)
The next step is to actually road test the vehicle, using the tester to make the appropriate shifts by selecting the shift on the tester. Not a lot to test on the A4LD but in the 4R and 5R you basically shift the entire sequence of shifts since they are computer controlled.
The real benefit in a tester such as this is you can isolate the transmission from the car computer and see if the problem lies in the computer inputs or within the transmission itself.
It is a VERY useful tool. Although it won't "diagnose" your transmission per se, but used in the prootocol FORD outlines can be a valuable ally in helping isolate the problem. Interestingly, I get a strong impression that FORD dealers rarely use it. Mine was bought off E-bay and is virtually unused.
I'll add some to this thread later. (maybe some a test of a fully computer controlled transmission - like say the AXOD-E, since I have no access to a 5R55E locally.) The overlay for the 4R and 5R makes the A4LD overlay look like a Dick and Jane novel. In other words LOTS more to do and check - see ?
[to be continued]
In the old days, transmissions never saw a single electron. They were hydraulic marvels controlled by engine vacuum, governors and throttle cables. With the A4LD, we saw inklings of electronic transmission control. (For those of us in the Ex community anyway... we always came last). In the A4LD, the OD (3-4) shift and the Torque convertor lockup were electrically commanded by the Powertrain Control Module (PCM, or Computer). Suddenly the ball game changed when it came to diagnosing what might be wrong, at least for those shifts, for everyone else many, or most, shifts were controlled by the computer....a mixed bag for diagnosticians of these magnificent contraptions. Today they are all virtually all electronically controlled.
[SOAPBOX MOMENT. I think the computer control of automobiles is the single most important improvement in the last 30 years. People say it's a conspiracy to keep the shade tree mechanic from working on his or her own vehicle but that isn't so. You just have to keep up with the times. No 60's mucsle car ever told you what system was ailing... and they got rotten mileage too. I love computers in automobiles. I find them useful and fascinating. ANd they are your FRIEND.. not your enemy... DO they sometimes make life a little tough? Yep, but work WITH them and you will save more time than you lose. OFF SOAPBOX.]
In an electronically controlled transmission, the computer might not be doing what it needs to do when it needs to, often mimicking a hydraulic or mechanical problem in the transmission, so the diagnostician often doesn't know which problem is because of the hydraulic system and which is the fault of onboard computers commands. So the first course is to separate and eliminate the possibility of bad computer commands. How? we substitute a human in place of the computer.
In the “for what it’s worth†category, this thread will deal with the way FORD wants their technicians to diagnose a FORD automatic transmission. I will show the use of their Transmission Tester, and discuss the pattern of diagnosis FORD promotes. While not many will have some or all these tools, the ideas presented and the knowledge of how it SHOULD be done might be valuable to those taking their vehicles to the dealer for help.
This thread is geared to the A4LD, 4R55 and 5R55 series of transmissions. The A4LD had little computer control, the 4R and 5R are practically ALL electronically controlled.
FORD has a basic diagnosis protocol. It is a good source of information – since the computer is controlling things, their first concern is to make sure every engine input to the computer is ok. SO you first check for Diagnostic Trouble Codes (DTC’s) on the engine and related sensors first, since many of these in turn drive the PCM commands to the transmission. Only once you are certain that the engine is trouble free do you move on to the transmission. Next you look for transmission DTC’s. Those you analyze and see if there is a direct issue you can fix. Failing that you hook up the transmission tester. What this does is allow you to disconnect the PCM from the transmission and directly command the transmission from the tester – eliminating any possible PCM issues. Then failing a fix, you work through hydraulic issues (using the Manual) and if that fails the FORD technicians had a help line to call. By then, it was/is probably rebuild time anyway – especially if all “non-trannie removal†attempts at fixing it had failed.
To start out, here is a great link about this issue – not FORD related.
http://www.babcox.com/editorial/bf/bf90222.htm
So with that under our belts, to start, here is the FORD protocol:
And here are the “tools†you need: A FORD Transmission manual, a high impedance voltmeter, a transmission pressure gauge, the Rotunda Transmission Tester with appropriate cable and overlay, and a scanner or code reader. A break out box is optional.
AS indicated, our first course of action is to scan the vehicle for Diagnostic Trouble Codes (DTC's). I have done a separate thread on scanners and code readers and I refer you there for accomplishing this task. (hint: put "Primer" in the search term)
Next step is to hook up the transmission tester itself. (FORD wants you to hook up a transmission pressure test gauge as well, but we'll omit that for what we are doing here - and there is a thread on that too). Each transmission has it's own special cable for hooking up to the tester. Locate the vehicle's own cable to the transmission and then unplug the vehicle transmission cable from the transmission and plug the tester connector in it's place. (You have now severed the umbilical, as it were) Like so:
The tester has "overlays" appropriate to the transmission you plan to test.
Here is the tester plugged into the A4LD with the A4LD overlay installed:
Notice that the overlay has 3 LED's on the top and those 3 LED's on the tester are illuminated. This means the tester is hooked up correctly. Now on the A4LD, the only things computer controlled are the TCC and the 3-4 shift solenoid. (not a lot in the scheme of things) We can test these and also test the diode in the solenoid setup. (For now accept that there is a "one way" street in the electrical system to run these solenoids ... we will test to see of the cop is doing his <ok ok, even her> job on that street).
Here we are testing the 3-4 shift solenoid resistance.... Notice the reading. Normal is 26 - 40ohms.
Similarly by pressing the button without an ohmeter hooked up, you could check the operation of the solenoid (the so called click test) and get a green light... I didn't get a picture of this so I'll post that later
Next I am going to turn to the TCC solenoid operation. (I was testing in the "bench" (as compared to "DRIVE") mode, so in esssence I am powering the solenoid and checking for any electrical issues.)
The TCC (here called the CCO - convertor clutch override - long story, all about how this circuit works, not important in this discussion) tests in the upper left quadrant of the tester. Here is the "green light" during the "click test".
Here is the resistance test for the same solenoid... again looking for 26 - 40 so this is a good pass.
The diode is tested by making a jumpered connection on the tester. Here I am testing the Diode (notice the LED is green - a pass- the one way street traffic cop is on duty)
The next step is to actually road test the vehicle, using the tester to make the appropriate shifts by selecting the shift on the tester. Not a lot to test on the A4LD but in the 4R and 5R you basically shift the entire sequence of shifts since they are computer controlled.
The real benefit in a tester such as this is you can isolate the transmission from the car computer and see if the problem lies in the computer inputs or within the transmission itself.
It is a VERY useful tool. Although it won't "diagnose" your transmission per se, but used in the prootocol FORD outlines can be a valuable ally in helping isolate the problem. Interestingly, I get a strong impression that FORD dealers rarely use it. Mine was bought off E-bay and is virtually unused.
I'll add some to this thread later. (maybe some a test of a fully computer controlled transmission - like say the AXOD-E, since I have no access to a 5R55E locally.) The overlay for the 4R and 5R makes the A4LD overlay look like a Dick and Jane novel. In other words LOTS more to do and check - see ?
[to be continued]
