Street Smart - May - 2019

Performance Codes: Knowing Where to Start

A Toyota Tundra, equipped with a 5.7L engine and an AB60E transmission, was dropped off with a complaint of no 5th and 6th gears. A road test revealed the costumer was right: no 5th or 6th.

So the next step was to scan the truck for codes. We find codes P2714 and P0776: both performance codes. The P2714 code is for the SLT solenoid, line pressure control. Code P0776 is for SL2 solenoid, pressure control solenoid B.

Way too often, a shop sees codes like these, jumps the gun and replaces the two solenoids without doing any testing, only to find it has the same problem with the new solenoids. That turns out to be a costly mistake.

Solenoids aren’t cheap, especially from Toyota. New solenoids run about $250-$300 each, plus the WS type trans fluid, new filter, and labor. All to discover that replacing the solenoids didn’t fix the problem.

Keep in mind that both codes are performance codes, so code P0776 can be the result of the SLT solenoid not supplying enough pressure to the SL2 solenoid to do its job, setting code P0776.

That can be misleading, since the SLT solenoid is failing to control line pressure as it should. And these solenoids have a high failure rate, so there’s a good chance you could run into this situation.

Any time you have a P2714 SLT solenoid performance code, followed by one or more solenoid performance codes (P0748, P0776, P2757), your best bet would be to perform a line pressure test (figure 1). Doing this as a starting point in troubleshooting can save you a lot diagnostic time.

Solenoid performance codes, such as P0748, P0776, or P2757 that follow a P2714 are sometimes known as ghost codes, because there’s nothing wrong with the solenoid itself. It just isn’t getting the pressure it needs to control its clutch circuit. That’s where checking line pressure is a big help.

Description

The ECM uses signals from the output and input speed sensors to detect the actual gear ratio: 1st, 2nd, 3rd, 4th, 5th, or 6th gear. Then the ECM compares the actual gear with the shift schedule to identify mechanical problems with the shift solenoid valves, valve body, or automatic transmission (clutch, brake, gear, etc.)

So, with low line pressure, the shift won’t occur in the timeframe programmed into the computer, and the ECM will see that as a performance problem.

To replace the pressure control solenoid D (SLT), you’ll need to remove the valve body. And, with the valve body off, that makes this a good time to air check the transmission (figure 2).

Remember: most customers don’t bring their cars in until they’re missing a gear, it’s burnt out a clutch pack, and gone into failsafe. At this point it’s probably too late to save the transmission. But if they’d brought it in when it first started acting up, they might have gotten away with just replacing a solenoid.

A couple things to keep in mind if you do an overhaul:

  • It’s a good idea to replace all the molded pistons. Even if they feel soft and pliable, they’ll shrink, be undersized, and will cause a delayed apply.
  • Keep an eye on the sealing ring. Some of the aftermarket rings are showing up undersized. If your rings look good, reuse them.
  • When doing air checks, only use about 25-30 PSI. You should be able to get a good air check at this pressure; using full shop air pressure can force a seal, misleading you into thinking the circuit is good.

Solenoid Performance Codes

The three things that will cause a solenoid performance code are:

  1. A solenoid is stuck open or closed
  2. The valve body is blocked or a stuck shift valve
  3. A transmission clutch, brake, or gear

We didn’t have any electrical codes on this Tundra. Let’s look at an electrical code and see the difference between that and a performance code.

Electrical Description

Here’s one: code P0778 is pressure control solenoid B electrical (shift solenoid valve SL2).

To shift from 1st to 5th involves a combination of operating shift solenoid valves SL1, SL2, S1, S2, S3, S4, and SR, controlled by the ECM. If an open or short circuit occurs in a shift solenoid valve, the ECM controls the remaining normal shift solenoid valves to allow the vehicle to operate safely.

P0778 indicates an open or short in the shift solenoid valve SL2 circuit. The ECM commands shifts by turning the shift solenoid valves on and off. When there’s an open or short circuit in any shift solenoid circuit, the ECM detects the problem, lights the MIL, and stores a DTC.

It also performs the failsafe function and turns the other shift solenoids that are in good condition on and off. In case of an open or short circuit, the ECM stops sending the current to the open or shorted solenoid.

After seeing what’s involved in a performance code, dealing with an electrical code might seem simple. After all, there are only two wires, so the diagnosis should be straightforward.

You have these areas to check:

  1. Transmission wiring
  2. Shift solenoid valve SL2
  3. Replace the ECM

Start at the computer: Unplug the connector and check pins 12 and 13 going to the transmission (figure 3).

If the wires check good for continuity, the next step would be to replace the solenoid.

If the solenoid doesn’t correct the problem, you’re only other possibility is the ECM. We can’t test it directly; we can only presume its failure if everything else is good. So that’s the last thing you should think about replacing.

And that’s not just smart, that’s street smart!