89 PA code 27

Searched the threads for code 27 but doesn't seem like it's common problem. Lots of issues with cams sensors and this machine is throwing a code 41 too. :(

Done one of those before. Code 27 is new territory though.

Following the flow chart in the service manual it calls for voltage and test light readings at the transmission cable and connector. I take it that's the 5 wire cable at the front. The drawing lists pins A-E. Anyone have pinout for the connector?

Where are these switches inside and what's involved in accessing them? I've worked on a Celebrity 4 cyl that had a bad solenoid. Is this similar?

TIA

Yes, you definitely need a schematic for a 4T60 transmission, showing the harness going in.....

The problem could be the harness to the tranny(broken or shorted wire), or the problem could be inside the tranny(second gear switch or the harness inside the tranny to the switch), or the ECM.....


Doing your electrical tests will determine which is at fault.....

Yes, you definitely need a schematic for a 4T60 transmission, showing the harness going in.....

The problem could be the harness to the tranny(broken or shorted wire), or the problem could be inside the tranny(second gear switch or the harness inside the tranny to the switch), or the ECM.....


Doing your electrical tests will determine which is at fault.....

Where can I get such a schematic? I have some of the drawings for the shop manual but it doesn't show the connector.

Some large city libraries carry these old manuals.....

Otherwise, just go to a Buick dealership, and have them make copies from an old manual they will have on hand...bring a "Coolata" for the Service Manager....

To my knowledge the 4t60 only used pcm commands for the TCC, not the shift points. 91 up was the "e" version that did have shift solenoids. BTW code 27 refers to Quad driver issues, that is what handles high load solenoids or relays in the powertrain, this may not be trans related at all.

Some large city libraries carry these old manuals.....

Otherwise, just go to a Buick dealership, and have them make copies from an old manual they will have on hand...bring a "Coolata" for the Service Manager....

I did find letters on the cable connector. Had to clean and look very carefully but they're there. Also the wire colors sort of match up with the drawings. Somewhat faded. Lt Be looks like green. :redface:

Will check the switches with a test light and meters as laid out in the manual. Will report back.

Code 27-
2nd gear switch was closed or grounded when vehicle was in 4th gear, or 2nd or 4th gear switch was
open when engine was first started.
Code 27 will set if:




No Code 29 pres:ent.
CKT 581 indicates ground or closed switch for 10 seconds when vehicle is in 4th gear operation.
CKT 581 indicates an open (drive) when the engine is first started.
CKT 446 is open when the engine is first started.49618

49619

Max , the tranny is shifted hydraulically.....these are switches, not solenoids....

And yes, the ECM quad drivers were sometimes the culprit, but the switches have to be checked out first, and the best place is at the harness connector at the ECM, with the connector disconnected from the ECM, that way you are checking the wiring to the switches and the switches at the same time....If you find a problem, then you continue with the harness connector at the tranny, to determine if it's the harness, the switch or the ECM...

Max , the tranny is shifted hydraulically.....these are switches, not solenoids....

And yes, the ECM quad drivers were sometimes the culprit, but the switches have to be checked out first, and the best place is at the harness connector at the ECM, with the connector disconnected from the ECM, that way you are checking the wiring to the switches and the switches at the same time....If you find a problem, then you continue with the harness connector at the tranny, to determine if it's the harness, the switch or the ECM...

OK, here's the latest. Used a test light on the tranny and second gear switch is open. Not good news. Orange wire on the connector (E). "C" and "B" are showing closed.

So it's inside we go and that's not happening for a few days. Maybe quite a few days. I was told by a wrecker buddy today that the cover can't be removed without dropping the sub ?? frame assembly, engine and tranny. :banghead:

Max , the tranny is shifted hydraulically.....these are switches, not solenoids....

And yes, the ECM quad drivers were sometimes the culprit, but the switches have to be checked out first, and the best place is at the harness connector at the ECM, with the connector disconnected from the ECM, that way you are checking the wiring to the switches and the switches at the same time....If you find a problem, then you continue with the harness connector at the tranny, to determine if it's the harness, the switch or the ECM...


What's involved here? Anyone have a picture(s) of the inside or links to working on these transmissions? I found a parts picture but I think it's for newer models in early 1990's.

What's involved here? Anyone have a picture(s) of the inside or links to working on these transmissions? I found a parts picture but I think it's for newer models in early 1990's.

Update:

Pulled the side cover off the tranny. This transmission has been replaced with what seems to be from an Olds. No idea what year or model. It has no second gear sensor. Instead that wire leads to a thermal device. 6K ohms at room temp and climbs when heated. So it's basically useless in this application and car. From all the trans shops I've consulted, this transmission in these older cars use no input from the ECM. The only thing the computer controls is the lock up solenoid. Everything happens hydraulically. One shop said I could probably get away with shorting that second gear wire to ground permanently. Take it for a test drive and see how it performs.

One thing I did do was temporarily short the wire to ground. If the second gear switch is open more than ten seconds after starting it will throw a code 27. Shorting it during that period prevents the code.

My plan now is do one of two options.

Add a timer circuit which keeps that circuit grounded for minimum 10 seconds after starting the engine.

Or add a simple relay with a normally closed contact grounding the second gear wire and when the vehicle is placed in drive the relay would pickup removing the ground. Essentially the same condition in which the vehicle is operating presently (sending a second gear condition continually).

Because everything seems to be working fine except it's throwing that 27 code because the switch is open during the first 10 seconds.

OK, here's the latest. Used a test light on the tranny and second gear switch is open. Not good news. Orange wire on the connector (E). "C" and "B" are showing closed.

So it's inside we go and that's not happening for a few days. Maybe quite a few days. I was told by a wrecker buddy today that the cover can't be removed without dropping the sub ?? frame assembly, engine and tranny. :banghead:

further update:

It's fairly easy to get access to the guts. Raised the front of the vehicle on blocks. Trolley jack under the sub frame to take the weight. Remove the steering shaft and exhaust. Disconnect the axle, tie rod, lower ball joint and sway bar. There are three large bolts on each side of the sub frame. Remove the inner rear only on the right side. Remove the three bolts on drivers side. Use blocks for safety in case of jack failure and slowly lower the drive side down about 4 inches. Oh, you will also have to remove the three transmission mount bolts at rear and two in front on the drivers side because the cover will not pass the sub frame on the bottom corner. The tranny has to be lifted slightly to make clearance. Not near as frightening as first glance. :biggrin:

Could be wrong here but isn't the 2cnd gear switch only closed when it sees apply pressure, so during a non operational check it would be open normally?

Could be wrong here but isn't the 2cnd gear switch only closed when it sees apply pressure, so during a non operational check it would be open normally?


No the reverse happens. NC contact. Second, third and fourth are all the same (in the original transmission from my research) and all open in sequence as the vehicle changes gears and accelerates. I was told the pressure to operate is low, perhaps 5 lbs. This replaced transmission omitted the second gear switch. It really doesn't serve much purpose anyway, perhaps affecting ignition and fuel injection but not the transmission. The vehicle doesn't operate long in these lower gears so there is very little advantage. Once fourth gear is reached all switches are open.

I'm reluctant to have a continually closed or bypassed switch because it may affect ignition and fuel delivery from the ECM. For that reason I will develop a work around as mentioned above.

I think someone posted the circuit and description from the shop manual earlier in the thread.

[edit]

See post #7 by Autojoe. It explains what happens. Second gear 581 org wire must be closed when first started. It must be open in fourth gear operation.

(so the possibility of shorting 581 org wire to ground permanently is out).

Finale:

Code 27 is cured. I dawned on me that if I shorted 2nd gear and 3rd gear together it would accomplish the same thing as a proper second gear switch and keep that circuit grounded for the 10 seconds required. Second gear switch would open along with third gear and not affect 4th gear as would a continually shorted 2nd gear switch. Only drove it about 3/4 mile and up to 35 kmh or so but it shifts nicely and no codes anymore.

Happy camper. So easy and here I spent a day pulling the dang thing apart and re-assembly.

Good job, most people would have given up on this, especially on an older car.

I do not see how that works.....

I do not see how that works.....


All switches must be closed for 10 seconds after starting the engine or it will send a code. By paralleling the second and third switches it accomplishes the same thing as having a good second gear switch. Second gear switch would normally stay closed for ten seconds and open as soon as it reached that gear. Now it must wait till the vehicle reaches third gear. Since this old transmission doesn't use any signals from the ECM it doesn't affect operation. All those switches do is control fuel delivery. Doesn't really matter all that much since you're normally in fourth and OD.

This vehicle doesn't have many miles on it. It was owned by an elderly couple. Body and interior are in good condition. Two tires are new. The other two are fair. Brakes are good. It needed a little TLC like ignition switch, power ant, RH mirror broken. I can get one from wrecker here for $15. Speaker wires were broken in the left door jam. Cam sensor magnet was thrown. Cost for parts $40. The transmission had the wrong reluctor wheel for the speed sensor for this car so the speed and mileage was quite a way's off. Whoever changed the tranny didn't save the old one. I got a used one which I'll have to check for accuracy. I found they come in several different sizes. Command start is missing remotes so I'll probably install a new alarm/command. Two new in box were advertised locally on the internet for $50.

Total cost for repairs won't be much over $100.

All I have left to do is the command start if I go that way and it's ready for the road. I may pull the Oxygen sensor to have a look and wheel alignment.

Had I known more about transmissions and these codes I would have saved a day's work. But it was worth the experience.

When I said, I don't see how this works, I meant the input signals to the ECM, indicating which switches are open and closed, indicating which gear the tranny is in......I know these switches are not used to shift the tranny, since this is a 4T60, not a 4T60E.....that is done hydraulically, not by the ECM....

When you start the car, all switches are normally closed.....since you have an open circuit with the 2nd gear switch circuit(either switch bad or the harness to it internally is open), by jumpering 2nd gear circuit to 3rd gear switch, yes you have removed the problem on startup....however, first gear will be ok....when you go into 2nd gear, that switch should open, and the ECM should see an open circuit, but it's not because you have jumpered this circuit to the 3rd gear circuit which is still closed.....

So, as far as the ECM is concerned, it "thinks" you have shifted from first to third to fourth......

When I said, I don't see how this works, I meant the input signals to the ECM, indicating which switches are open and closed, indicating which gear the tranny is in......I know these switches are not used to shift the tranny, since this is a 4T60, not a 4T60E.....that is done hydraulically, not by the ECM....

When you start the car, all switches are normally closed.....since you have an open circuit with the 2nd gear switch circuit(either switch bad or the harness to it internally is open), by jumpering 2nd gear circuit to 3rd gear switch, yes you have removed the problem on startup....however, first gear will be ok....when you go into 2nd gear, that switch should open, and the ECM should see an open circuit, but it's not because you have jumpered this circuit to the 3rd gear circuit which is still closed.....

So, as far as the ECM is concerned, it "thinks" you have shifted from first to third to fourth......

The ECM doesn't get any change signal until the vehicle shifts to 3rd. It doesn't matter. The only thing the signals are used for is fuel delivery. I pointed that out. It's minor. This transmission doesn't HAVE a second gear switch. Whatever vehicle it came from (Olds) didn't care too much about it apparently. That ECM must not have monitored second gear at all.

I don't understand your concern or argument.