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So I’m working on a 95 Chevy k1500 4×4 with the 350 TBI and 4L60E. My main issue is that when the transmission fuse is pulled, the wire from the ignition switch provides sufficient voltage (12-14). But as soon as I place the transmission fuse in, the voltage from the ignition switch drops to either 1.4 or 5.6 volts. Am I looking at a possible short? Or an ignition switch issue? I can provide more information as necessary. I will not replace anything until I can get some help to confirm (99%) what the issue is. Thanks for any help you can provide.
Engine: 1.5 years old; was a new crate
Transmission: New one swapped in 6 years ago
Total mileage on body: 220k
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Transmission fuse protects the transmission and instrument circuit 1020. On the transmission the Trans fuse protects shift solenoids; A, B, 2, 3 and the tongue convertor clutch solenoid. The fuse feeds(B+) 12 volts through terminal “E” at the transmission connector. The PCM grounds the circuit(s) through transmission connector terminals B, A, S and T and PCM terminals F10, E8, E9, E11 and E10.
I would check for PCM and transmission codes. The transmission shift solenoids are issues with that transmission, but that’s not saying that’s your problem.
Let me know if you need more information.
I ran the codes first and they were all the shift solenoid codes and the TCC code. Which is why I started looking from the ignition switch, the fuse, and wiring.
If you had a bi-directional scan tool it would help with diagnosis…but hopefully I can help…
The transmission fuse is the ignition switch voltage for that circuit. When the ignition is in the on position Battery + voltage is sent to the Trans fuse. The circuit path is from the ignition switch through connector 266 ,terminal 1 Pink wire (left side of steering column near firewall bulkhead connector) through firewall bulkhead connector 100 terminal E2 (behind under hood windshield washer Pump, ABS BPMV, under hood fuse relay center) pink wire to fuse box trans fuse.
In my opinion I think your Ignition switch is ok if you have B+ voltage to the Trans fuse. I would isolate the Trans fuse circuit and do an (Resistance) Ohm’s test with a DVM to see if you have any wiring issues in the circuit. (Remember to disconnect all voltage from the system to do a resistance test).
As a quick check disconnect the round transmission connector and see if the voltage drop goes away. If it does, you’ve confirmed a good circuit from the ignition switch to the Transmission connector. If it does not check the wiring circuit like I stated in the previous paragraph.
The ground side of the circuit is the PCM; which is transmission connector terminals B, A, S and T and PCM terminals F10, E8, E9, E11 and E10. To test those circuits you’re going to have to make some jumper wires (from connectors to terminals) and disconnect each terminal until the resistance goes away.
Remember the PCM grounds the circuit to make it function. If the wiring harness for that circuit is grounded from transmission connector terminals B, A, S and T and PCM terminals F10, E8, E9, E11 and E10 anywhere you will complete the circuit and cause voltage potential / amp flow.
If all that checks out ok…the next step is inside the transmission…let me know if you need help with that.
I talked to a friend who went to UTI for transmissions and currently specializes with GM Hydromatics. He suggested that doing an ohm test on the solenoids first. Also directed me to a site for a procedure on the entire issue: http://www.trutechtrans.com/Topic-1-00-01.html
It says: Check resistance of 1-2 solenoid with your meter from terminal A (LT GRN) to terminal E (PNK or PNK/BLK). Resistance value should be 20 to 30 OHMs. Then check resistance of 2-3 shift solenoid with your meter from terminal B (YEL or YEL/BLK) to terminal E (PNK or PNK/BLK).
I didn’t have a spare harness so I used small alligator clips and a DVM. The harness letters didn’t match up to the colors. So I tested both ways. Pink was on C, yellow and light green were on F and G. No resistance on anything at all except terminals A and D. A didn’t have a wire on the harness and D was black. Making me think that the part the the harness plugs into has failed. But with the wiring being different, who knows. Hope this helps you to help me out. Thanks
Ok I changed a couple of colors to match a ’95. See attached picture for correct terminal location for a ’95 C/K truck 4L60E transmission.
Check resistance of 1-2 solenoid with your meter from terminal A (LT GRN) to terminal E (PNK). Resistance value should be 20 to 30 OHMs. Then check resistance of 2-3 shift solenoid with your meter from terminal B (YEL/BLK) to terminal E (PNK). Value should be 20-30 OHMs. A quick test of solenoid operation; with the transmission harness disconnected and the test harness attached apply 12 volts to terminal E while grounding terminal A or terminal B listen for the clicking of the solenoid. If resistance values are different or solenoid does not “click” when powered replace solenoid.
I’m going out for the rest of the day. Hopefully I’ll be back later tonight…anymore problems just ask.
OK I understand that you have a strange voltage drop at the ignition switch, but what issue are you trying to solve? Do you have a no start condition? A transmission that doesn’t shift properly?
Just trying to get a better handle on what the issue is that you’re trying to address.
Sorry it took me a while to reply, busy with work.
The issue is that the transmission (4l60E) is in limp mode. The codes the computer gave me were all solenoid related. I know that the TCC can cause the rest of the solenoids to stop working (based on the wiring diagrams I’ve found). I’ve confirmed that the harness has proper power. I’ve replaced all the solenoids as well as the harness inside the transmission (also ohmed the solenoids). If I’ve got adequate power to everything and I know the solenoids are in spec, all that’s left is PCM (ground drivers inside it for the trans solenoids) right?
Eric: It starts up and drives fine. I’ve checked other possibilities for poor performance and they are all good. Unless I shift the shifter to first or second, it’s in third gear. Reverse works well, but acts like it’s in second gear. It’s really easy to test which gear the transmission is in as I live in the mountains in Montana. So luckily there’s a noticeable difference between gears.
A quick test of solenoid operation;(with out a scan tool) with the transmission harness disconnected and the test harness attached apply 12 volts to terminal E while grounding terminal A or terminal B listen for the clicking of the solenoid. If resistance values are different or solenoid does not “click” when powered replace solenoid.
If the solenoid’s click, you have to find out if the PCM is commanding a ground to the circuit.
I’m going to my shop; I’ll get a service manual and post the wiring diagram later for the circuit from the PCM to the transmission.I know all the solenoids work. Ohm tested the new solenoids and checked the new harness inside the transmission. That’s all good.
I’d appreciate the wiring diagram from the PCM to the Trans. Thanks.
Thanks for the diagram and information. Sorry it took me so long to get back, my brother was in town visiting for a week. All the wiring (colors and pins) matched so I’m confident it is wired the same as stock.
For my results. For E8-11, I got the exact same reading both KOEoff and KOEon, they were 30 mV. So either I’m not getting power to the solenoids or the ground drivers aren’t working. I tested the ignition source to the PCM and I was getting 12+ volts.
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