Another needle in a haystack: Locating wiring problems - Transmission Digest

Another needle in a haystack: Locating wiring problems

Paul Loch from Certified Transmission wrote a very good and detailed article for Transmission Digest in the March 2022 issue entitled “A Needle in a Haystack – Finding and Diagnosing Intermittent Problems.” The vehicle used for this article was a 2013 Ram 3500 6.7L equipped with a 68RFE transmission. Well worth the read.

ATSG encountered a similar story recently, when ATSG technician Bob Bloomquist worked with Matt at Matt’s Transmission, who went looking for a needling problem with a 2011 GMC Sierra 2500 HD with the 6.6L diesel powering a LCT 1000 transmission. It originally came in with both slip and electrical codes. After inspection it was apparent that the transmission needed to be replaced. They ordered a Jasper reman transmission and installed it. Once in, one code remained: code P0962 for low voltage with the Main Modulation/Line Pressure Control Solenoid.

With a completely different transmission, they carefully inspected the solenoid harness connector first. With no signs of any problems there, the technicians pulled a wiring diagram like the one shown in Figure 1.

Figure 1.

The wire in question is the dark blue wire that runs from terminal S at the transmission harness X175 connector to the 80 pin MW7 Transmission Control Module connector.

Note that the TCM is in the front engine compartment near the fan shroud. Due to aftermarket serpentine belts causing a significant amount of electrostatic charge on their surface, the TCM may have been relocated to the top of the UBEC cover. The same thing happens if it is equipped with an upfitter package and extended belts causing them to be closer to the TCM.

Due to the location of the TCM, the wiring harness to the transmission is routed through the driver’s side fender. To find where this wire in compromised is like finding a needle in a haystack. The only upside is knowing that the needle is dark blue in color.

Matt chose to locate where this wire was shorted or deteriorated rather than running a new wire bypassing the problem. This required removing the inner fender to get a better look at the harness. In doing so, he noticed that the harness looked as if it has been rubbing in the area of the upper control arm as seen in Figures 2 and 3.

Figure 2.
Figure 3.

After unraveling some tape to expose the area where the rub took place, he used a mirror to examine the wire (see Figure 4).

Figure 4.

After much time and tedious effort, there it was: a dark blue wire which was rubbed into and shorting out (Figure 5). Matt found the needle in the haystack.

Figure 5.

In ATSG’s 2023 seminar, one of the subjects we cover is a 2007 Dodge 2500 with a 68RFE transmission that intermittently sets a P0871 Overdrive Pressure Switch Code. My intro slide says: “Looking for a Needle in the Haystack.” The hold-down bracket for the harness (Figure 6) had rubbed into this wire and would intermittently short it to ground, setting the code.

Figure 6.

As you can see in Figure 7, it was a very small rub through, making it difficult for Chris Harmon to find it; but he did. And so, I use this example in the seminar to provide a few pointers of where to look for this needle in the haystack.

Figure 7.

If you encounter this problem then, as Matt and Chris did, you should look for areas where the harness could be rubbing. These include hold-down brackets, suspension components, body seams, bolts, screws, flashing, etc.

Another area to look for is where the harness can be affected by heat, such as exhaust leaks blowing hot exhaust onto the harness, or that the harness has dropped too close to the manifold or catalytic converter. Look for battery acid or water compromising connectors. When checking for power and grounds at a connector, oftentimes we back probe. Don’t forget to check the face side of the connector as well. I have seen situations where there was good power supply to a TCM connector on the back side, yet on the face side there was a sever voltage drop causing the computer to malfunction. Connectors can be compromised internally.

Another thing to look for is where the wires go into the back side of the transmission connector. When they fatigue due to heat, after unplugging the connector to remove the transmission, they break in this area. Sometimes if you peel away the conduit, you may also find that the wire insulation has deteriorated and now bare wires are exposed and touching each other.

These are just a few tips to help relieve you from a needle that can poke you, making for an irritable day.

Read more stories from our Technically Speaking column series here.

You May Also Like

Back with force: ATSG is back in full swing to educate the transmission industry

“Everywhere you turned, there was something amazing. It’s probably the coolest man cave I’ve ever been in,” says Wayne Colonna who, as president, heads up the technical team at the Automatic Transmission Service Group (ATSG). Wayne is describing the host venue for his company’s inaugural 2024 seminar that was held at the John Force Racing

“Everywhere you turned, there was something amazing. It’s probably the coolest man cave I’ve ever been in,” says Wayne Colonna who, as president, heads up the technical team at the Automatic Transmission Service Group (ATSG). Wayne is describing the host venue for his company’s inaugural 2024 seminar that was held at the John Force Racing facility and museum in the Los Angeles suburb of Yorba Linda, California. Transtar’s Orange, CA branch served as the presenting host for the event.

Ford 8F35 maintenance tips: Planetary failure and no-pressure conditions

Our shop has had several vehicles come in with the Ford 8F35 transmission having planetary failure. Apparently, there was a run where the pinion needle bearings had a hardness problem (see Figure 1). Related Articles – Don’t fear customer complaints about CVTs – 2024 State of the Powertrain Industry – Powertrain industry directory and buyer’s guide

Figure 12.
Don’t fear customer complaints about CVTs

Continuously Variable Transmissions, or CVTs, are more common than you think. Audi, Subaru, Nissan, Ford, GM and many other automakers use CVT transmissions in cars and SUVs. There is no way to avoid them. Chances are there is one in your shop right now. Related Articles – Shift Pointers: A Chrysler 300 no-shift complaint –

Shift Pointers: A Chrysler 300 no-shift complaint

The case study has to do with a 2009 Chrysler 300 C 5.7L Nag1 RWD with 71,923 miles on it (see Figure 1, above). Related Articles – Sometimes, a diagnostic code is all you need – 10L80 and 10R80 pump gear differences – Top 20 Tools and Products: The Winners It is based on a

A guide to common GM, Ford and Nissan programming issues

One of the most common complaints I hear from shops when trying to install a new GM TCM is, “The module will not communicate.” While that might be partially true, by design they won’t communicate until they are programmed. If programming fails, there will be an “E” code set which will help you get to

Other Posts

Schaeffler, ATSG partner to support technical education

Schaeffler announced that it has entered into a partnership with the Automotive Transmission Service Group (ATSG) to become its primary sponsor. Through this agreement, Schaeffler will provide ongoing technical education support to the members of ATSG, which has offered technical support and repair information for transmission technicians for nearly 40 years. Related Articles – ALI

TransGo highlights 68RFE valve body reprogramming kit

TransGo highlights its new tuneless high-pressure performance valve body reprogramming kit for the Chrysler 68RFE automatic transmission. It is designed for Ram trucks with this transmission, model years 2019 and on. The company highlights the fact that users do not have to remove the transmission to use the kit. Related Articles – PRT launches 59 new

Diagnosing Ford 10R60, 10R80 and 10R140 series speed sensor issues

Ford 10-speed 10R series transmissions utilize four two-wire, Hall-effect sensors — TSS, ISSA, ISSB and OSS — for providing speed signals to PCM or TCM. They are supplied nine volts by a PCM or TCM and assist in the control of clutch apply/release timing that is used in determining shift quality, including TCC. Related Articles

Jatco JF613E transmission quick reference material

For those working on the Jatco JR613E transmission, a widespread transmission with plenty of applications, the following should be a helpful guide. Related Articles – Hidden problems: Three tales of electrical issues – Easy TH400, 4L80-E reverse servo setup: Craft your own tool – Outgrowing the walls: The story of EVT Transmission Parts Domestic and