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Gears Magazine | From the Ground Up
On the Road - October/November - 2017

From the Ground Up

It’s difficult trying to keep up with all the technology in today’s cars and trucks. So much so that sometimes it can feel overwhelming. And when a problem shows up after a repair, it can complicate things even more.

We’ve all had our nightmare vehicles that never seem to make it out of the shop… the jobs that never die. Check this, check that, change the solenoid, change the valve body. Hey, maybe it’s the computer! If I had a dime for every time someone replaced a computer for no reason, well, I wouldn’t be rich, but I’d have a lot of dimes!

In this issue, we’re going to check for faulty grounds to correct slip and bind problems on some Toyota vehicles. You know: those vehicles with U140 and U150 transmissions… the ones with all those computer problems.

I know, you’ve heard it before: Always check grounds. It’s one of the first things you do. And it’s one of the first things we remind technicians who call the ATRA HotLine.

Sometimes the technicians are a step ahead: They’ve already checked the battery ground, cleaned the battery terminals, inspected the bellhousing and engine block ground connections, and maybe even replaced the terminal ends. All with the idea that these steps should correct any ground issues.

Many times it does. Sometimes it doesn’t. That’s usually when the wallet comes out and the shop starts buying parts, which gets expensive and, more often than not, doesn’t fix the problem. And that’s usually when they call the HotLine.

So what’s the secret? Where are these guys missing the mark? Let’s look at an actual call that came into the HotLine: The technician was having a heck of a time trying to correct banging shifts on a 2007 Toyota Sienna.

We’ve had several calls like this over the past few months, each with Toyota Siennas with erratic, hard-banging shifts. These were all rebuilds and the guys did the work right. They rebuilt the transmission with new parts, a new converter, and the proper fluid. They reset the transmission memory using a capable scan tool. Still, the harsh shifts remained.

So, before you check the grounds at the battery, body, engine and the transmission; before you replace the solenoids, valve bodies, and computers, we have your answer: The most commonly overlooked failures are the splices and junction connectors.

Splices and junction connectors aren’t new. They’ve been around pretty much as long as wiring has been going into cars. What’s interesting is how often technicians take these problem areas for granted. They aren’t relegated to just Toyota vehicles, so this basic information pertains to pretty much all cars. But today we’re talking about the Toyota Sienna with U150.

IDENTIFYING GROUND CIRCUITS

Look at the wiring diagram (figure 1). This is a typical trans mission wiring diagram for a 2007 Toyota Sienna that shows the ground circuits. At first glance, you see two ground points: EB and EC (figure 2). This is typically where ground circuit troubles take place.

The technician checks EB and EC ground points with a meter, and cleans or repairs them until a voltage drop test indicates less than 0.1 volt with the engine running. This is also where the ground checks typically end. But that isn’t enough; you’ll often need to look further to find and correct ground problems.

Let’s take another look at the wiring diagram (figure 1). There are three inline connector points and a splice:

  • J20 junction connector
  • I13 junction connector
  • J48 junction connector
  • Splice point 22141

If there are issues with any of the terminals or wires at these connections, it’ll compromise the computer ground and you’ll have excess voltage in the ground circuit. We’ve seen voltage readings on a computer ground wire greater than 0.11 volts cause problems.

So a proper ground path is important. How do you get there? You could look up each splice and junction connector location and the connector views, and you could check the connectors and wiring for corrosion, loose terminals, chafed wires, and the like. All of which can take literally hours and hours of searching through the Toyota web site.

Where are these connectors located?

  • J20 and J48 connector (figure 3)
  • II3 connector (figure 4)

The splice locations are hard to find. Knowing what to look for will help you diagnose the concern easier.

TESTING GROUND CIRCUITS

So you could access each of those junction connectors and search the harness for the splice, or you could choose the easy way, by probing the wires at the back of the computer connectors. Here’s how:

First, locate the computer, which is under the right side of the dash behind the glove compartment (figure 5).

Next, begin backprobing the wires at the back of the computer to check for voltage to ground. Refer to the computer connector layout view (figure 6) and follow these steps for checking the grounds.

For each test, voltage should be below 0.1 volt; 0.1 volt or higher indicates a poor ground. And check these circuits with the engine running, to make sure the circuits are under load.

  1. 35-pin E5 connector — backprobe pin 35 with your meter’s positive lead. Connect the negative lead to the battery negative terminal.
  2. 32-pin E11 connector — backprobe pin 1 with your meter’s positive lead. Connect the negative lead to the battery negative terminal.
  3. 34-pin E9 connector — backprobe pin 6 with your meter’s positive lead. Connect the negative lead to the battery negative terminal.
  4. 34-pin E9 connector — backprobe pin 7 with your meter’s positive lead. Connect the negative lead to the battery negative terminal.
  5. 35-pin E10 connector — backprobe pin 3 with your meter’s positive lead. Connect the negative lead to the battery negative terminal.
  6. 35-pin E10 connector — backprobe pin 4 with your meter’s positive lead. Connect the negative lead to the battery negative terminal.
  7. 35-pin E10 connector — backprobe pin 6 with your meter’s positive lead. Connect the negative lead to the battery negative terminal.
  8. 35-pin E10 connector — backprobe pin 7 with your meter’s positive lead. Connect the negative lead to the battery negative terminal.

REPAIRING GROUND CIRCUITS

Once you’ve identified any ground circuits with more than 0.1 volt, you need to repair those faulty circuits. One way to do that would be to trace the circuit back, find the loose or corroded connection, and repair it.

An easier fix would be to run a redundant ground wire to the computer. Here’s how:

Choose the wire with the excess voltage. You’ll need to strip back some of the insulation from the wire, and splice a second ground wire into the circuit. Since this is inside the passenger compartment, you shouldn’t have to get too crazy about sealing the repair.

Always use a wire that’s at least the same gauge as the wire in the harness. You can use a heavier wire, but avoid using a lighter gauge wire.

Once you have the wire connected to the computer circuit, run the other end to a good engine or chassis ground. Some people might suggest running it back to the battery, but battery terminals are more susceptible to corrosion, and can cause problems later. A main chassis or engine ground should provide adequate ground for the circuit.

Make sure that you don’t leave any of the wires loose that go to the junction connectors (figure 7).

Once you’ve checked and repaired the computer grounds, the transmission should begin operating properly.

In the Siennas we’ve seen over the last few months, the most common ground problem was with pin 35 on the E5 connector. On each of these vehicles, the voltage was less than 0.4 volts; twice it was less than 0.2 volts. That may be because that wire goes through each of the junction connectors, so there’s a greater capacity for increased resistance. When the technician ran redundant grounds to a chassis ground, the shift problems vanished.

While it’s a great idea to check grounds at the body, frame, engine, and transmission, if the computer isn’t grounded properly because of poor connections through splices and inline connectors, the problem will remain.

So don’t overlook ground checks at the computer. It could save you a lot of time and money, and it’ll definitely help your vehicle’s computer stay grounded.