Author Topic: 1986 gmc 6.0/4L80 oxygen sensor and trans codes??  (Read 3154 times)

Offline 86charcoalsierra

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1986 gmc 6.0/4L80 oxygen sensor and trans codes??
« on: April 10, 2020, 05:00:18 PM »
I have a 1986 GMC sierra I recently did a swap on from a 305 with turbo 400 to a 6.0/4L80 out of a 2002 Chevy Silverado 2500hd. this is the first swap I have done so I'm pretty new to this. I left the original harness on the 6.0 and just wired in the essentials to get it to run and drive no modifications were done to the harness except splicing in power wires ignition wires from the original 1986 harness. I'm using the fuse block out of the 2002 Silverado. I recently drove it around for about an hour and a half with a heavy foot. my coolant temperature stayed around 200 which is normal but my transmission temperature got up to 225 I'm thinking this is kind of high not dangerously high but I'm told it should run at about 175-200 is this true? I have a trans cooler in the radiator thinking of going with an external. what are yall transmission temperatures usually run on a nice sunny day? also, I am getting these codes p0706-trans range switch performance, p0753 1-2 shift solenoid control circuit, p0758 2-3 shift solenoid control circuit, and p1860 torque converter clutch solenoid control circuit. I'm wondering if I forgot to wire something in does anybody has any idea. truck runs good shifts smoothly but when I step on it doesn't feel like its downshifting it just goes instead of downshifting and then going.

I'm also getting oxygen sensor codes p0134 and p0154. I got the rear o2 sensors tuned out and I'm getting voltage to sensors. does anybody have a wiring diagram for the o2 sensors so I can check for ground and signal. or any idea what else might be causing these codes. thanks in advance for any help.

Offline JohnnyPopper

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Re: 1986 gmc 6.0/4L80 oxygen sensor and trans codes??
« Reply #1 on: April 10, 2020, 05:34:32 PM »
Can't help with the codes, sorry.

About the heat, did you service the trans as in oil and filter? Overheating can be caused by poor circulation.

I bet you miss that quick 305... ::)
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Offline 86charcoalsierra

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Re: 1986 gmc 6.0/4L80 oxygen sensor and trans codes??
« Reply #2 on: January 14, 2021, 10:24:51 PM »
Update on transmission problems I figured out when I wired everything up I didn’t put power to transmission wire on connector c100 pin c. Which powers all the shift solenoids It was in limp mode didn’t notice until I got a chance to drive it around a little more. Also installed a tru-cool transmission cooler now trans temp is way lower. Now it downshifts when I step on it has a lot more power.

Also been reading that I need to install a tcc brake switch for torque converter has anybody ran with out it. The stand alone harnesses I’ve been seeing are not wiring up for it.

Offline VileZambonie

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Re: 1986 gmc 6.0/4L80 oxygen sensor and trans codes??
« Reply #3 on: January 15, 2021, 07:55:35 PM »
You want the TCC to disengage when you hit the brakes so yes you need a TCC brake switch. lots of options including the factory style brake switch for vehicles with lockup converters.

An auxiliary trans cooler can be added but you should still run the factory cooler as it is designed to regulate the fluid temperature at a more stable temperature.

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Offline frotosride

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Re: 1986 gmc 6.0/4L80 oxygen sensor and trans codes??
« Reply #4 on: March 25, 2021, 06:26:45 PM »
You shouldn't actually need a switch. The OEM PCM has a TCC lock /unlock signal wire. Check the pin outs on to find the right one for that 2002 PCM. Once found you can use the OE brake switch.

Before I got to you last post my first thought was you forgot ignition power to the trans range switch.. glad you figured that out. That so also the reason your trans temps were so high. But I you are going to be towing then the external cooler will be a trans saver.

Good to see someone making progress on their swap.
"Beat it like a red-headed ford"
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