Diagnosing AS68RC intermittent pressure switch/linear solenoid performance codes - Transmission Digest

Diagnosing AS68RC intermittent pressure switch/linear solenoid performance codes

Intermittent pressure switch codes on vehicles with the Aisin Seiki AS68RC transmission have been very difficult to nail down to one specific cause. The two most common pressure switch codes for this transmission are P0746 clutch pressure control solenoid A or linear solenoid A performance or “Stuck Off,” which also includes pressure switch 1 mechanical fault. The second-most common code is P0776 clutch pressure control solenoid B or linear solenoid B performance or “Stuck Off,” which also includes pressure switch 2 mechanical fault. What typically happens is that the diagnostics start with the definition of the trouble code on the scan tool.

The code definitions shown above are the full definition of the code and honestly, if we don’t take the time to get that full definition, we will only get the first four to five words in the sentence. If we are really lucky, we will get the word “performance,” which refers to a mechanical problem in the hydraulic circuit of the solenoid, per the definition on the scan tool. Commonly, the words “pressure switch” will not be listed on the scanner.

Interestingly, the Dodge Ram truck P0746 code lists clutch pressure control solenoid A or linear A performance first; but Mitsubishi applications list pressure switch 1 as being at fault, with no mention of linear A performance.

Furthermore, if we go into OE diagnostics for Dodge, it takes us through five different monitor conditions that are connected to five different set conditions — very thorough, but very complicated. The worst part of it is that the possibilities of the root cause are actually inside this virtual piñata full of maybes. The list includes a harness problem with pressure switch 1, a bad pressure switch 1 or a problem with control valve 1 (which happens to be immediately behind linear solenoid A). It also lists an internal mechanical transmission problem and, of course, a bad TCM.

The issue here is that you may not have access to OE diagnostics, and you have replaced linear A or B solenoid three times, which keeps coming back with this same code intermittently. Without the OE diagnostics, it is like your brother moving the rope for the piñata every time you take a swing with your trusty Louisville Slugger.

Let’s break this down so we can make some kind of sense out of it, now that we have a full description of possibilities. It seems like the common denominator for this code points to a pressure switch problem of some sort, whether it be mechanical, in its hydraulic circuit or a bad connection with the switch. To explain this correctly, we need to first look at the hydraulic circuit to see the items in play. Figure 1 (above) shows a partial circuit diagram of linear solenoid B when it is at high duty cycle.

This solenoid’s output pressure acts on control valve 2. Notice, in Figure 2, that when linear B duty cycle drops, control valve 2 moves to the right and connects line pressure to clutch apply pressure.

Tasc-Tips-May-Figure-2---Linear-Solenoid-B-at-Low-Duty-Cycle
Figure 2.

At the same time, clutch apply pressure is directed to a damper valve and pressure switch 2. Believe it or not, this damper is the most common root cause of a pressure switch 1 or 2 code. Regarding the damper piston, the bore on which the piston rides becomes worn out and allows pressure to leak past the piston. This pressure loss can affect how quickly the pressure switch responds or closes. This, in turn, causes a trouble code to be set, as the TCM thinks the pressure switch is stuck off. The TCM commanded a gear change, and the pressure switch in charge of feedback to the TCM did not change state quick enough. Both dampers connected to pressure switches 1 and 2 oil circuits are identical (Figure 3).

Tasc-Tips-May-Figure-3-Damper-&-Pressure-Switch-Locations-1400
Figure 3.

Figures 1 and 2 also show that there is a damper connected to the solenoid feed circuit which can also wear. These pistons can be easily checked by vacuum testing the exhaust port by the spring end. Wear can also be seen in the bottom of the bore. Figures 4 and 5 show a cross-sectional view of the damper pistons and the location for vacuum testing.

Tasc-Tips-May-Figure-4-Vacuum-Test-the-Exhaust-Port-in-the-Casting-1400
Figure 4.
Tasc-Tips-May-Figure-5---Exhaust-Port-Locations800x700
Figure 5.

Note: When vacuum testing these pistons, be sure that the vacuum reading does not drop when moving the piston from side to side, as this indicates a worn bore. A new piston and casting will test 20-plus-in.-Hg, and worn bores can go as low as 4-in.-Hg. There are also relief pistons in the upper valve body that are for cooler relief and a solenoid feed relief. These two locations can be vacuum tested in the same way: by vacuum testing the spring side exhaust port on the back side of the casting.

This same vacuum testing process can also be performed on AS66RC and AS69RC applications, as they can experience similar wear in the three relief valves.

Jim Dial is a Sonnax technical specialist. He is a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax technicians.

Read more columns from the TASC Force Tips series here.

Was this content valuable?

Thanks for your feedback!

You May Also Like

The importance of the follow-up road test after transmission replacement

A 2002 Lexus RX300 equipped with a 3.0-liter V6 engine and U140F transmission was brought into our facility with a few concerns. The customer said that “it has a leak, a grinding noise when taking off from a stop, and it just doesn’t seem to shift right.” They went on to tell us that this

RR Tech Feature Oct

A 2002 Lexus RX300 equipped with a 3.0-liter V6 engine and U140F transmission was brought into our facility with a few concerns. The customer said that “it has a leak, a grinding noise when taking off from a stop, and it just doesn’t seem to shift right.”

Tips and tricks for Chrysler switch valve plug testing

As technicians, we are often faced with build issues that can sometimes be frustrating at first. But with a little ingenuity, these frustrations can be turned around and made simple. Related Articles – GM 8L90 #7 Check-ball: The overheat that saved the day – ETE Reman: Ever expanding – Shift Pointers: Nissan’s no throttle response

tascfeature-1400
GM 8L90 #7 Check-ball: The overheat that saved the day

Beginning in October of 2015, GM removed the #7 Check-ball from the solenoid valve control body in the 8L90 transmission (see Figure 1). This was done in conjunction with the elimination of the Lube Override Enable Valve from the upper valve body as shown in Figure 2. Related Articles – Jatco/Nissan JF011E critical wear areas

Shift Pointers: Nissan’s no throttle response

Nissan vehicles using continuously variable transmissions (CVTs) are notorious for defaulting to a no throttle response when the vehicle is engaged into gear. There are several malfunctions that can cause this protective failsafe feature to be initiated. A brake switch (stop lamp switch) stuck on, a double-footed driver, blown or incorrect brake bulbs, and wheel

Jatco/Nissan JF011E critical wear areas and vacuum test locations

Sonnax has provided the following guide on critical wear areas and vacuum test locations for the Jatco/Nissan JF011E. Technicians working on these models should find this guide helpful. (Ed. Note: This is an extended version of the guide found in our September issue, with three additional pages). Related Articles – Podcast: Talking CVTs with Transtar,

Other Posts

Sonnax highlights GM 4L heavy-duty input shafts

Sonnax highlights its line of heavy-duty input shafts for GM 4L transmissions. The company touts the torsional design that allows energy to be absorbed, reducing peak loads to critical areas. Related Articles – Gray Tools releases insulated socket sets – RatioTek introduces new tuner kit for Ram trucks – GFX introduces Ford, GM steel packs

Sonnax-74678S-HD-1400
Sonnax introduces Ford 6R140 bypass blocker valve kit

Sonnax has introduced a new bypass blocker valve kit for Ford 6R140 transmissions, model years 2011 to 2016. The company says this kit is made to replace the faulty thermal element lineup in these transmissions to prevent the potential of overheating. The kit (part no. 126740-26K) includes a drop-in Zip Valve for installation. Related Articles

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 – ATI introduces pressure

Sonnax introduces new five-inch splined stub and sleeve kit

Sonnax has introduced a new aluminum splined stub and sleeve kit designed for 1350 series u-joints. Sonnax says this kit is designed for Ford trucks, including the Super Duty, among others, and allows users to raise the torque capacity of the driveshaft. The kit is part no. T35-125-500-KIT. Related Articles – Raybestos offers high carbon