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Old 12-03-2004, 06:25 PM   #1
levon63
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Unhappy 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!
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Old 12-03-2004, 08:00 PM   #2
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Re: Service Engine Light Soon 1997 LT Blazer

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.
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Old 12-03-2004, 08:44 PM   #3
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Re: Service Engine Light Soon 1997 LT Blazer

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.
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Old 12-04-2004, 10:53 AM   #4
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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.
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Old 12-04-2004, 02:28 PM   #5
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Re: Service Engine Light Soon 1997 LT Blazer

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.
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Old 12-04-2004, 07:34 PM   #6
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Re: Service Engine Light Soon 1997 LT Blazer

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
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Old 12-04-2004, 10:18 PM   #7
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Re: Service Engine Light Soon 1997 LT Blazer

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
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Old 12-04-2004, 11:05 PM   #8
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Re: Service Engine Light Soon 1997 LT Blazer

Aha, what luck, thanks for posting as backup.

I knew I remembered someone having this solution.
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Old 12-05-2004, 07:37 AM   #9
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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
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Old 12-05-2004, 08:31 AM   #10
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Re: Service Engine Light Soon 1997 LT Blazer

Excellent....

Wish more people knew this, no one would think a switch causes a tranny problem.
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Old 12-13-2004, 10:11 AM   #11
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Service Engine Soon light

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?

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Old 12-13-2004, 10:13 AM   #12
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Re: Service Engine Light Soon 1997 LT Blazer

Just the switch will be fine.
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Old 12-13-2004, 09:15 PM   #13
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Thumbs up Service Engine Light Soon

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.
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Old 12-13-2004, 09:25 PM   #14
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Re: Service Engine Light Soon 1997 LT Blazer

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.
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Old 12-13-2004, 09:40 PM   #15
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Re: Re: Service Engine Light Soon 1997 LT Blazer

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.

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Originally Posted by BlazerLT
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.
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