Hidden problems: Three tales of electrical issues - Transmission Digest

Hidden problems: Three tales of electrical issues

In this article, I will discuss some vehicles with electrical issues. These issues were previously addressed by a different shop/tech, but the improper or incomplete repair resulted in these hidden problems that would appear later.

The first case was on an early 2004 Chevrolet Venture FWD, with a 4T70 transmission. This van was setting solenoid codes and faulting into limp mode. After removing the intake air filter box for access to the harness, the potential cause became fairly obvious when I spotted what looked like dried hot glue in a corner of the wire harness branch. (See Figure 1).

Figure 1.

With a swipe of my thumb, the hard glob of glue rolled off the harness, revealing a wire that had previously rubbed through to bare wire and later became corroded from exposure. Apparently, the application of the hot glue was a previous attempt by someone to cover the bare wires and protect them from any additional contact or corrosion. Obviously, this was not a sufficient seal and the wire corrosion shown in Figure 2 was the result. 

Figure 2.

To correct the harness issue properly, it was necessary to open the harness breakout, splice in new wire with soldered connections, seal with heat shrink tubing, and re-tape for support. After clearing the trouble codes, I took the van out for a road test and the transmission was operating properly, with no codes being reset. The repair was successful, and the vehicle was released to the customer.  

My second case involved a 2003 Ford F-150 with a 4R70W transmission. Its concerns were that the check engine light was on, the O/D lamp was flashing, and it wasn’t shifting. During the preliminary checks the truck was setting shift control codes, but not until it was driven a distance, at which point it would eventually fault into limp mode. 

During a visual check I could see heat damage to the wire harness near the right-hand exhaust manifold. The harness wasn’t contacting the manifold like I typically see when the harness retainer at the rear of the right-hand head is either damaged or not reconnected after service. The harness had been supported away from the manifold, but the damage to the harness had not been repaired. I chose to address this first as it would need to be corrected regardless of any relationship to the customer concerns. 

After disconnecting the harness connectors and retainers, I pulled the harness down under the truck to access the damaged portion and I found that the damaged heat shield tape had chafed through the wire insulation, shorting two circuits together in the harness itself. (See Figure 3).

Figure 3.

After cutting out and replacing all the chafed and heat-damaged wires, the split conduit and heat tape were replaced for protection and retainers were installed to keep the harness away from harm. A final road test confirmed that the customer’s original concern was repaired and the transmission was performing properly.

The final case I wanted to write about today was a late 2007 Silverado 2500 equipped with a 6.6L Duramax engine and Allison 1000 six-speed transmission. This truck was setting control codes with erratic shifts and neutralizing at times with the shift indicator flashing. A visual inspection of the harness and connectors didn’t reveal any obvious problems. 

Clearing all codes and road testing reproduced the solenoid codes and limited the gears commanded from the computer. In addition, after setting for a short while with the hood closed, the shift indicator would flash in some ranges with no gear commanded, but also no range switch codes set. 

Next, I started testing the circuits for short to ground and/or power at the TCM connector with it disconnected. I followed that by testing the circuit resistance through the solenoids. With no problems found there, I moved on to testing the range switch circuits. These responded to each position correctly. Disconnecting the harness from the transmission, I inspected the connector, tested each circuit back to the TCM connector for resistance, and did a pin drag test to all terminals with no problem found. 

With both connectors now treated with dielectric grease, I again drove the truck and after getting to operating temperature, confirmed that the concern was still present. I was still unconvinced that the problem was internal to the transmission. I had a used TCM handy for this model, so I decided to install and program it to the truck. Much to my disappointment (but not surprise), the condition was still there. Feeling ready to throw in the towel, I took some time to walk away from this job and regroup. 

When I circled back to this truck, I decided to let it idle with the hood closed and build heat in the engine bay before re-testing. After I felt that sufficient time had passed to warm the circuits, everything still re-tested OK from the TCM connector, so I closed the hood and let it idle a bit longer. 

I later shut the engine off, disconnected the transmission connector, then raised the hood, and disconnected the TCM to isolate the circuits. Before testing from connector to connector, I tested between each of the circuits and found high resistance bleeding between a couple of them. Moving the harness changed the resistance reading. Next, I slowly massaged the harness and found the meter reacted the most at a low point in the harness close to the TCM, and a little below the corner of the right-hand battery.

Now my eyes focused on some light corrosion on the battery tray. It looked like some old acid damage that had been neutralized and cleaned up, and I also noticed some white residue on the harness conduit that could have also been acid damage. Hoping that this was the clue that I missed up to now, I proceeded to open the harness and witnessed some wires with the insulation swollen and softened. (See Figure 4).

Figure 4.

With the damaged wires cut out and new spliced in, I used battery cleaner and brake clean to flush out the inside of the conduit before closing it. With all codes cleared I took it on a longer road test. I then let the truck idle at the shop for a while, drove it again, performed a 20-minute hot soak, then restarted, and took a short drive with no codes reset, and correct transmission performance. Cue my happy dance.

I don’t know that I should blame someone else for a poor or partial repair on this one, but the root cause was repaired prior to this condition arising, which showed the need for us to make the most thorough and complete repair possible. Over the years of doing this I have come to dislike crimp connectors; even the crimp and seal can cause a variance in resistance with temperature. With electrical architecture ever-evolving, your skills and methods of wire repair are going to become even more important—but that could be another article in itself.

Read more stories in our R&R Tech series here.

Gordon Kehler started working as an auto technician in 1975, achieved his ASE Master certification in 1985, L1 in 1994, and has kept them current to date. He held GM master tech certification from 1991 to 2019. He joined the Certified Transmission team in 2019 as a Diagnostician. He and his wife of 40 years have raised three children and have six grandchildren.

You May Also Like

Shift of the shaft: Diagnosing Chrysler 48RE manual shaft issues

The TorqueFlite transmission has been around since mid-to-late 1950s. There have been many changes surrounding the manual shaft and rooster comb through the years. This transmission shaft controls the position of the manual valve that directs oil for the gear ranges, but it also is used for a Reverse light control as well as Park/Neutral

The TorqueFlite transmission has been around since mid-to-late 1950s. There have been many changes surrounding the manual shaft and rooster comb through the years. This transmission shaft controls the position of the manual valve that directs oil for the gear ranges, but it also is used for a Reverse light control as well as Park/Neutral safety control. As it evolved, changes to these safety backup switches caused extra stress against the rooster comb that posed new challenges to the technician. 

Going the extra mile: Proving your transmission repair suspicions

A 2003 Honda Pilot with a five-speed three-shaft transmission came into our shop with a customer concern that the vehicle had no power, and the “D” light was flashing. I first did a scan for codes to see what it came up with, and the scan tool returned four DTCs: P1298 (ELD voltage high), P0135 (H02S

How reading through service bulletins can turn a technician into the customer’s hero

Over the last 28 years of being a technician, I have developed the habit of checking for and reading technical service bulletins at the forefront of the diagnostic process, especially when an unfamiliar vehicle exhibiting blatant or straightforward concerns comes into the shop. I have found many valuable nuggets of information while reading over these

Looking deeper: Telling apart electrical issues and parts issues

We see such a variety of transmission problems these days, and all the electronics involved today certainly have added a whole new crop of potential issues. Even though a significant part of our diagnostic process is geared towards electrical issues, there are still times when the problem is simple and not related to electronics at

Sonnax introduces Sure Cure Kit for GM 6L80, 6L90

Sonnax has introduced a Sure Cure kit for rebuilders of GM 6L80/6L90 transmissions. The company says this kit can restore shift quality and repair common TCC trouble areas, offering products to help rebuilders repair worn areas and protect the transmission against future damage. The kit is part no. SC-6L80-6L90. Related Articles – Force Control Industries

Other Posts

Easy TH400, 4L80-E reverse servo setup: Craft your own tool

While not as sensitive as some shifting bands, the Reverse band adjustment on a TH400 or 4L80-E transmission is critical, and failure to get it right has tripped up even the best builders. There is nothing worse than getting the transmission installed, putting it in Reverse and then not going anywhere or having no engine

Outgrowing the walls: The story of EVT Transmission Parts

There’s an interesting business, one of our industry’s success stories, located in the greater Los Angeles area city of Compton, CA. Walter Quintanilla is the owner of EVT Transmission Parts, which supplies a full line of parts and supplies to rebuilders in the area and beyond. The company began as a Los Angeles transmission shop

Spotting different 68RFE designs through the years to avoid issues

The Chrysler 68RFE has had several changes through the years. Its four-speed predecessor began with a noisy solenoid pack identified by a black colored pass-through case connector (seen in Figure 1).  Related Articles – Fabricating frictions: Keeping ahead of the curve at Raybestos Powertrain – Shift Pointers: Focused DTCs – Vote for the Top 10

Valve body and component suppliers: A comprehensive list

Looking for a comprehensive list of the industry’s valve body and valve body component suppliers for 2024? TD has you covered. Below, find a list of suppliers including contact information, addresses, etc. Related Articles – Manual clutch repair and diagnostics – Manual transmissions in 2023: Some are still sticking with it – Inside Toyota’s UA-UB80E/F torque