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Discussion Starter · #1 ·
My 93 4WD Suburban (4L60E) will not shift into low or OD except when cold and usually forcing it to shift by manually moving the shift lever. I checked the voltage on all the solenoids at the computer and they all appear OK except the 3 to 2 downshift. I also shorted the solenoid pins to ground and they all "click" except the 3 to 2 downshift. Would this keep the tranny from shifting into low or OD? I am trying to figure out if I have a tranny problem or a computer problem????
 

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check the transmission atf and filter

otherwise, i had a problem in cold whe i tried to put D from P. But in hot the gears fuction perfectly. I changed de transmission atf and filter.
 

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Discussion Starter · #3 ·
ATF and Filter

The transmission is recently rebuilt and only has about 6K miles on it. Fluid is bright pink not burnt at all.
 

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i had similar problem with mine would downshift and upshift when i was crusin around 45mph you might wanna change the shift solenids that cured my problems mine tested just a hair low when i check them out
 

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Well I finally found what was causing the shifting problem. The connector on top of the tranny could be rotated about 1/4" in the tightening direction when I rotated the connector it would shift correctly when I turned it back the tranny would go back into the "limp" mode. The truck has been OK for about 12000 miles now.
 

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I'm having the same problem on my '94 K1500 4WD Silverado with 4 speed automatic transmission. When I put it in drive it will start in 3rd gear and not shift into O/D. I can start it 2nd gear by shifting to 2nd with shift lever and then hand shifting to drive for 3rd. It will not shift into 4th gear (O/D) at all. When it's cold if I put it in drive it will start in 1st and then shift into 2nd and 3rd on it's own as it should, but at the first stop sign it will revert back to starting in 3rd gear when in drive.

I will look for this connector thing that kwwood1 mentioned. Does anyone have any other experience or ideas about this type of transmission behavior?
 

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Solenoid A and B on/off states
1st gear,. ON ; ON
2nd gear, OFF ; ON
3rd gear,. OFF ;. OFF
4th gear,. ON ; OFF

If solenoid A has no power, it's OFF all the time and solenoid B is good, these will be the scenarios.
1. When tcm commands 1st, A and B will be OFF: ON and this will be second gear. You will have no first gear.
2. When tcm commands 2nd, it's already in second gear, OFF:ON
3. When tcm commands 3rd gear, B is good and will turn off, OFF:OFF. This is 3rd gear.
4. When tcm commands 4th gear,
A is still off and B is off, state is OFF:OFF, and it's still in 3rd gear. No 4th gear/overdrive.

Check transmission connector integrity to check A solenoid 12V power and ground connections and resistance.
Google 4L60e connector pinout to perform the test.
 
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I just want to add that the tranny dosent receive ground like we would normally think, through the case. instead it gets one 12V+ through pin E, a pink wire, this wire also is the wire that runs up through the tranny (prndl) fuse and then to the ignition switch, then to the big ass main harness plug on the firewall and so on. all the other wires are the negative, ground switched leads that operate the solenoid functions.

do you have ANY other symptoms? check engine lights or codes?

your symptoms are frustrating and being that it's a 94 I'm not entirely familiar with the obd1 symptoms of a failed ignition switch. but I went through the same intermittent shyt with my 97 burb and it turned out to be the ignition switch. when the tranny (pin E) looses power or dosent recieve the same voltage as the battery it goes into limp mode. it should read the exact same voltage as the battery. limp mode can be caused by a bad connection at the plug, a blown fuse or faulty ignition switch. a blown fuse can be cause by an O2 sensor as the O2 heater is tied into the same circuit. limp mode is 3rd gear starts but can manually shift through the gears to get moving. no speedo. no prndl indicator light. and a check engine light with faults for every tranny circuit so like 6-7 tranny codes.

anyways I just wanted to throw out my experience, I have no idea what symptoms the 94 with an obd1 are.....

good luck!

Al
 
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hey thanks for the feedback you guys. I appreciate it. I've been fixing my vehicles for 50 years but I'm not a mechanic. I've just replaced a lot of parts. I've never had any training so your input really helps, especially your detailed explanation bazar01.

I failed to mention that I did take it to a transmission shop. They replaced the ignition switch, but they couldn't get a switch that worked! Shortly after they installed the new switch it stopped making contact and I had to get out and jump the starter solenoid with a screwdriver to get it going. I think they used NAPA. The shifting problem persisted with the new switch. Then they tried installing a new computer, but the problem still persisted. They just told me flat out that they couldn't fix it. I liked the guy at the shop and I know he is honest so I will take your messages to him and see if he is willing to try again. I don't have any equipment to test the solenoids. I will research where they are and consider replacing solenoid A. According to bazar01 that is most likely the problem.

I have never gotten a check engine light with this issue.

Thanks again for your replies, Bert
 

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If its solenoid A/B issues or any solenoids, there will be a hard fault code, open driver, short to power short to ground or open circuit.
Get the transmission scanned.
Solenoids are inside the transmission.
Google 4L60e shift solenoid wiring diagram if you want trace the 12V @thegawd wrote at pin E. It's circuit 1020.
 
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Does your check engine light come on when the key is first turned to perform the light bulb test?

all electrical problems with the 4l60 will light up the CEL. since I wasnt sure what OBD1 codes may actually set I had a look through the list. obd1 dosent have nearly as many codes as obd2 and no, you wont get a code for each transmission electrical circuit. I would bet that the transmission shop is not entirely familiar with early obd1 4L60E'S but no doubt it's well within their capability as long as they start with proper knowledgable.

I believe if you have a failed ignition switch in an OBD1 system you should have at least a code 96 which is low transmission voltage. but since I do not have one of these trucks anymore I cant verify that. that code should light up if the transmission fuse is pulled, same with a failed ignition switch or bad wiring on Pin E.

I bought 3 ignition switches from low mileage trucks in a you pick junkyard. I gained lots of practice doing it to. your ignition switch is more than likely year specific but I could be wrong. the ignition switched in the junk yard are acdelco.... no idea what is available for your truck but I could have spent up to $300 on an acdelco, instead I spent $35 on 3 of them and a bonus bucket of goodies.

However I think I would bet money that your ignition switch and wiring are fine. what i didn't see on the list was any codes for failed solenoids or there electrical circuits. I would replace both if this tranny is not very old or if it is original I would have it rebuilt tough as hell.

Al
 
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