Diagnosing Automatic Transmission Problems, Preliminary Checks
You might be somewhat limited when it comes to diagnosing automatic transmission problems. In addition to the special tools you need to repair them properly, there are also special tools for diagnosis. One of the main tools is an automatic transmission pressure gauge.
This is one of the main diagnostic tools for automatic transmission problems. If you do have one of these tools, great. You’ll also need the service manual, which can tell you where to check the pressures as well as what those pressures should be. There are several pressure ports on the transmission. Knowing which ones to check and what pressure you’re supposed to see is a big part of automatic transmission diagnosis. If you don’t have access to an automatic transmission pressure gauge set, or the service manual information, here are a few general tips to get you started.
The first thing is to be able to differentiate between an automatic transmission problem and an engine performance problem. Much of this is covered in the Engine Performance Article, but I’ll go over it again here briefly. One of the easiest ways to find out if it’s an engine performance issue or an automatic transmission problem is to do a power braking test. In this test, you put the vehicle in drive or reverse, set the parking brake, hold your foot on the vehicle brake, and floor the gas pedal. The RPMs should top out somewhere in the 1500 to 3500 RPM range and hold there. If it’s an engine performance problem, it will likely show up here, as you are putting the engine under an extreme load. You don’t want to do the test for too long for that very reason, as you could overheat the engine. You’re just performing a check here, you’re not trying to blow up your engine.
Another test you can try if you’re having a shifting problem is to shift the transmission manually if possible. Some automatics have the ability to move the shift lever through the gears manually one at a time. Some only allow you to shift from second, but that’s better than nothing. The point of this test is to see if the transmission acts normally when you shift it yourself. If it does, this might indicate a problem with some of the automatic transmission controls and not the actual gears themselves.
This might or might not work on transmissions that have the upshift/downshift or sport mode feature. With these transmissions, you can take manual control of how the transmission shifts; they’re mostly referred to as sport shift or something like that. This is basically a manual override, but it still uses the same electronics to shift the transmission as it uses in automatic mode. What I’m talking about is physically moving the shifter from gear to gear, not just using paddle shifters or a special mode for the shift lever. You might get results shifting with sport shift, but as I stated, these modes use the same electronics to shift the transmission as the automatic mode does and you’re not moving the manual valve in the transmission that mechanically selects a gear. Because of this, you won’t get the same result.
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9 thoughts on “Diagnosing Automatic Transmission Problems, Preliminary Checks”
mitja
October 3, 2022 at 5:53 pm
Hey to all.
i have problems with my
– 2004 subaru forester 2.0 XT
– 240k km
– automatic transmission
it doesn’t shift gears. works reverse and 1st gear, but doesn’t shift up. car has been to 4 different mechanics and none of them was able to fix the problem, which lasts now for 5 months. i have made few mistakes when problems started (bought 2nd hand trasmission and changed it, changed ABS..) doesn’t work. i have now started to really search the net as none of the mechanics give any special effort into it. so i found you.
do any of yous have any idea what might be the problem?
before problems started, made few strong noises when i really floored the gas pedal in second gear on very high rpms (sound like crash/boom..horrible sound) and shifted into 4th (skipped 3rd gear).
after this last event, i got stuck by the road with possibility to drive in 1st or reverse.
any answers or suggestions of diagnosis are much appreciated.
bests from Slovenia
mitja
Justin mcomie
June 26, 2021 at 10:02 pm
Need help with my automatic transmission, I swapped it out and it went in fine but after it warms up it wont grab a gear but does when it’s cold anyone have an idea
Norberto
January 25, 2021 at 2:18 pm
NEED HELP! I have Honda 2002 Accord automatic with just 301,000 miles. Engine is still strong. I’ve had this problem since 190,000 miles +/-. Tranny slips from 1st to 2nd only. I change gear manually and on low rpm so it won’t slip. I can down shift to 2nd and 1st with no slipping. No codes pop up. I tested the solenoids and they are ok. Could it be just wear or have I missed something? Thank You for your prompt advise.
Kim juhani Pakkunen
October 25, 2020 at 2:40 pm
Ford S-max 2011 powershift gearbox, works fine in 1st and reverse but no other gears works. Any ideas? Thanx
Michael Anderson
May 8, 2020 at 2:03 am
I’m not sure if I’m doing this right. I have a 2006 Hummer H3 with the automatic transmission. I had it rebuilt about a month ago and yesterday I drove about 16 miles on the freeway and when I got off and was at a red light, when it turned green I went to drive like normal and it would only go 9 miles an hour. I finally made it home and tried 1st 2nd and 3rd gear and everything was sluggish no power. Reverse works fine. After letting it cool off, the next morning I went to drive it and it drove fine so I drove it directly to the transmission shop. I’m still waiting to see what the problem was but I’d like some input on what you guys might think it is. That way I don’t get more burned. It was full rebuild. Only thing original is the case I guess.
Alain Echeverria
July 15, 2020 at 2:10 am
Hello Eric,
I have a 02 Honda civic EX automatic transmission. I turn on the car put the car in reverse, drive and my car doesnt move. I removed all the selenoids and cleaned tested the with resistance oms test and they are all within range. Applied power to them and they all work. What else can I check?
Alain Echeverria
July 15, 2020 at 2:11 am
Also there is no codes.
Caleb Martinez
March 22, 2020 at 3:16 am
Hi i have a 97 honda civic with transmission codes. P0700 for transmission control system and p0758 shift solenoid b. Transmission shifts rough but does shift gear to gear manually. Kinda stuck not sure if i should try replacing solenoid b or ecu. Any help would be appreciated.
David Allen Johnston
May 23, 2020 at 11:15 am
I would start by testing the shift interlock and the B solenoid, it’s tested by adding 12v to each of the input while it is grounded. it will make a clicking sound if good and while you do that check the wiring connections for problems. While running those checks pull the solenoids and check the screens that filter incoming fluid, they might just be blocked with sludge. if all that checks fine, then see if you can convince a shop to cheaply test the TCM. Everything except the final task is cheap or free, and doesn’t take much time, mine was the interlock solenoid failing with oil soaked plugs shorting.