Can some one help me to test the external wire harness for resistance. I am not doing g something right. I can test and get 12 volts at pink wire. Now I want to check for resistance. I tried checking with DMM set to ohms. Tried to test for the solenoids. T to E, A to E, B to E, S to E and U toe. I am not getting any readings. There has to be resistance on something. Tried with key on and off. 2004 trailblazer. Please help if you can. I am trying make sure the external harness is good before going into removing g pan to test solenoids.

 

A little late, but here goes. The external harness goes from the trans to the PCM, the internal harness is the one that has the solenoids connected to it. If you unplug the external harness from the trans and check the connector, you should have 12 volts at the pink wire (E) and you should not be getting much of a reading from any of the others as you are reading the PCM circuits.



To check the solenoids you have to connect your meter to the internal trans harness connector on the trans itself. Easiest way to do this is to make a test connector, simply cut the external harness off one at a junk yard and label each wire with a masking tape tag with the terminal letter. Strip the end of each wire and connect the meter to the proper wires to test a particular solenoid. Plug it into your trans and you should get the correct readings if the solenoid and internal harness are OK. You can also back probe the external harness while it is plugged into the transmission (key off) and measure the resistance that way. With the PCM attached the readings may be off a few ohms though. The solenoids attached to the E terminal should also show 12 volts on the other terminal with the key on.


If you're getting solenoid electrical codes but the solenoids test good at the trans connector, you need to check for the same readings at the PCM connector to verify the external harness wiring between them is intact.


Also, take a mirror and a flashlight and check the terminals inside the trans connector. The pins can be damaged or even pushed down into the connector, creating a bad or no connection.

 

first time user, i have electrical codes . transmission has only reverse, 2nd, and 3rd. replaced internal harness and all solenoids.



I would like ohm values from external trans connector to pcm.

 

What are the codes?

If you are just checking the wiring between the trans and PCM, one probe on the trans end and the other on the PCM end connector, it should be low, like a couple three ohms or less. All should read within a few tenths of the other. Better test is to use a headlight bulb, make a jumper wire to apply the power from the pink wire, terminal E, to the other wires one by one. Attach one lead of the headlight to ground and touch the other to the wire at the PCM connector that you supplied with power. Should light the bulb brightly, only leave connected for a couple seconds though. The wires are small gauge, don't want to overheat them. Sometimes a bad connection only shows up under a load, if the bulb lights the wire is capable of powering the solenoid. Also, be careful you don't stick a probe down into the actual terminal in the connector, just touch the tip. The PCM side terminals are especially small, the probe can expand the connector to where it no longer makes contact and you have introduced a new problem.

Give me the year, make and model with engine size and I can download you a diagram of the PCM connector.

The normal operation is both solenoids on for 1st gear, A goes off and you shift to second. Both go off, you get third when B turns off. Turn A back on and you get 4th. If the A solenoid is not turning on you take off in second gear, no change when the PCM commands second, and shifts into third as the B solenoid goes off. A doesn't come back on for fourth, you stay in 3rd.

 

Hey, thanks for responding. The codes are: P0740, P0753, P0758, P0785, P2761, Truck is a 2005 Silverado K 1500. I was checking the wires on the external side of the disconnected trans connector and i have 12volts on pink and some crazy erratic voltages on most of the others to the pcm. My truck/tranny is in limp mode.

 

i changed all solenoids, harness, and now the external connector. no change

 

5.3 engine

 

Well, you have multiple solenoid codes, which 99.9% of the time means the solenoids are fine, just no power to them as that is all they share in common. Very unusual for 2 to go out at the same time, let alone all of them! Now, did you clear the codes and they all came back? Unplugging the connector to check it will set the codes.

 

Now there are only 3 codes. p0740, p0785, p02761 I was checking the grounds and found that when I disconnect the ground wires that are under the driver side door, on the frame, the truck dies and they spark pretty good when touching them to the frame. could this be a short to ground? or a super high draw on that little wire?.....Also, i was checking the transmission wires under the hood and when i checked the tan/blk wire, the light lit up very dim. I test drove it last night and it was still in limp mode and i could not reset the codes. This morning i got in it to take my boy to school and after resetting the codes, they didnt come back. Its done this before. It may work for an hour, or it may work for two days, but it has always thrown the codes again. Ive been reading everywhere about changing the ignition switch. What do you think about that? I also forgot to mention that the abs and brake lights have been on since i got the truck. I think its a bad ebcm.

 

Forgot to say that i do have 12 volts at the connector to the tranny.