Service Engine Light Soon 1997 LT Blazer

I had to go to auto zone twice and the second person knew what they were doing. The codes I had were:740,758,753 & 1860. My problem is I don't know where the wiring harness is to check for the 12V, short, or open? Also now that the light comes on my key gets stuck in the ignition? Can anyone tell me where the harness is? Thanks!

You should be looking for the ignition harness, the electrical part of the ignition switch is probably your problem. It is usually under the steering column directly above the brake pedal, a big rectangular connector that is bolted together(3" x 6", mayby 4x7). If I had a blazer available I'd post a pic, but I talked my brother into trading his off.

P0740 Torque Converter Clutch Circuit Malfuction
P0758 Shift Solenoid B Electrical
P0753 Shift Solenoid A Electrical
P1860 TCC PWM Solenoid Circuit Electrical

Make sure you connections on the ECM are nice and tight and make sure they are pressed in all the way.

Also, check that ignition switch, it is a problem on all 1997 s-series trucks.

With those codes you need to check the harness at the transmission (passenger side above the pan) Though those look like typical valve body error's. 95-99 4l60e's have common valve body issues and replacement with the updated versions usually take care of it.

True, but a lot of 1997 owners are having the same problems but oddly enough, they are somehow connected to the faulty ignition switch.

Don't ask me how, but one guy here a while ago swapped it out and the transmission problems vanished.

If you doubt the possibility of an ignition switch causing the problem, pull the trans fuse out and then turn your ignition switch on, start the vehicle and go for a drive, then check codes. The trans fuse is powered directly by the ignition switch, there is a TSB for fullsize 98 and newer TSB # 01-07-30-002C and it may superceded by "D" now. I have repaired a few fullsize made before 98 that had an ignition switch problem causing these codes. Best bet is to remove the big transmission harness connector and test for power(12V) on post E with the ignition switch on- check to see if post isn't backed out if there is 12V there. If there isn't 12V at connector check for 12V at trans fuse(or vehicle equivalent- fuse has changed names for different years) and then test white wire that is part of the ignition switch harness and both red wires(If a red wire in the ignition switch harness fails to have power any time the battery is not disconnected, you have a problem

As Blazer LT, said it is probably the ignition switch.
I would not have believed it myself but i had the same thing wrong with mine several months ago

my problems:SES light coming on, lack power when starting from a dead stop(If I shifted down to 2nd it would go) then shift to Drive when rolling

I went to autozone to get the codes which were :
P0758 solenoid B,
P0753 Solenoid A,
P0785 Shift timing solenoid,
P0740 Torque converter clutch,
P1860 Transfer case contact plate D.
I thought my 97 Blazer needed a new tranny and even the guy at autozone did to. I did some research and heard where others had this problem (one guy even got his tranny replaced just to have the same problem) and realized it was the switch.

I would suggest replacing it and go from there. If it fixes your problem great, if not then you just saved yourself some trouble down the road. Trust me 97 Blazers have a bad switch(I replaced a friend of mine's too for other reasons).
Good Luck

Aha, what luck, thanks for posting as backup.

I knew I remembered someone having this solution.

When I see these codes
P0758 solenoid B,
P0753 Solenoid A,
P0785 Shift timing solenoid,
P0740 Torque converter clutch,
P1860 Trans slip

and a customer also complains about a slow or sluggish take off, most likely the ignition switch is at fault.
There is also a GM TSB on this #01-07-30-002D

Excellent....

Wish more people knew this, no one would think a switch causes a tranny problem.

I have the same problem on my 97 Blazer. I just bought it and was thinking of giving someone a deal on it. After reading the forum I am as I write this on my way to purchase a new ignition switch becausemy blazer it doing the very same exact thing mentioned at the beginning of the forum. I had dire thoughts about this thing too; bombing came to mind. Also I was wondering if the ignition harness should be replaced during the switch replacement?

derblazer

Just the switch will be fine.

I replaced the ingition switch tonight 12-13-04 adn i fixed the transmission problems and a few others I had on the list too. The dash gauges fluttered a bit, especially the gas gauge and now it doesn't. I does seem pretty logical when you look at the wiring from the switch and see that it runs solinoids that govern the key.
Thanks for all the input.
PS.... It's not an easy job to replace the ignition switch if you aren't mechanically inclined have someone else do for you.

WAY TO GO!

Better than replacing the transmission eh?

Tough job but a cake walk compared to what you could have replaced without the advice.

Glad to help you.

Yes it was, THANK GOD; and much cheaper too. I did a huge GULP and almost hyper-ventilated when they told me the price of the valve body. My Blazer is a builder so I guess I'll be looking at this forum quite a bit in the future. I have noticed you post a lot of replies here.

WAY TO GO!

Better than replacing the transmission eh?

Tough job but a cake walk compared to what you could have replaced without the advice.

Glad to help you.

Yes it was, THANK GOD; and much cheaper too. I did a huge GULP and almost hyper-ventilated when they told me the price of the valve body. My Blazer is a builder so I guess I'll be looking at this forum quite a bit in the future. I have noticed you post a lot of replies here.

I do because I like to help, pure and simple. No other reason I would post close to 3500 times.

Hehehe.....

Hi, I am new to this forum and realize these particular posts are very old. BUT, it is exactly what I was looking for! My 97 Blazer problems are, SES light, very low power from start and my ignition switch acting up. We can actually start her up with out the key at times as the switch doesn't turn all the way off.
Of course we assumed we had 2 diff problems going on.Ignition switch and trans. Most pressing first would be trans. So, we had the trans fluid and filter changed with no results. Was about to change torque converter as we were told this could be the problem. (process of elimination)
Never, would we had thought the ignition switch was causing all these problems!
We are going to get on this asap, and I will get back with results.
I am so very grateful to this forum, and to all of you who made these particular posts. You may have saved us loads of money we don't have!:bigthumb:

My dad was the original owner of my Blazer then my brother who did nothing but drive it for 8 years then me. I do all the maintenance. Been a mechanic all my life. When my brother had it he had the dealership put a new ignition switch in it. I think that was either 2008 or 09. 2 months after I bought it from him, the trans went so I had it rebuilt. At 25,000 miles, it's time for a trans service and the check engine light comes on. It's code P1860. My transmission guy said drop the pan again and see if a connector came off a solenoid. I was pretty ticked when all is fine in the pan. To my surprise, I see a bunch of mentions about the ignition switch. It just so happens that for the last 6 months it's been screwing up and I can't get the key out once in a while. But...what I wanna know is why did the check engine light finally come on after I dropped the pan and put a new filter in it? Who can tell me that? What's really coincidental is that I ordered a new switch from ebay and it came in the mail yesterday. So, time to replace that and see what happens. I have an emission test to do and just because the check engine light is on even if it's got nothing to do with the way the engine runs, they will not pass it.
I found the problem. My trans guy was right. Always check the wiring before replacing the trans pan. I knocked one of the connectors loose to a solenoid and it looked like it was still connected. LESSON LEARNED!:runaround: