Diagnosing Transmission Solenoid Performance Trouble Codes

Jan. 1, 2020
There are numerous differences between manufacturers and transmission types, so we will be looking at a specific transmission and its operating system to try to keep it simple.

Diagnosing transmission solenoid performance trouble codes can be confusing, to say the least. The ATSG tech hotline receives many calls throughout the day related to this topic, and typically the caller is searching for the answer to this question: “Is this an external or internal transmission problem that I can easily fix?”

Figure 1

To even begin to answer this question, we need take some time and look at some of the components and criteria that a transmission controller is monitoring to set a solenoid performance code. As you probably already know, there are numerous differences between manufacturers and transmission types, so we will be looking at a specific transmission and its operating system to try to keep it simple.

First things first, what is the definition of a solenoid performance trouble code? I am going to go out on a limb here and give a semi-generic description. A solenoid performance trouble code typically will be explained on a scan tool as a solenoid, and its hydraulic circuit, that is either stuck off or stuck on. Some manufactures might just call it a solenoid performance trouble code without any clues as to whether it is stuck off or on. A solenoid and its hydraulic circuit pertains to the solenoid and the oil that is feeding it and the solenoid control pressure, which might control a clutch directly or indirectly through a clutch regulating valve. So what we are looking at is one solenoid and its mechanical performance, which also includes the ratio of the commanded gear. After all, when a solenoid or combination of solenoids are commanded to provide a specific gear, the control unit will need to see this gear by monitoring speed sensors which calculate the ratio.

Figure 2

This now brings up another question. Could a clutch that has a leak or a set of smoked frictions in it cause this performance code to set? Absolutely. Could this be a problem with the solenoid itself? Yes, it very well could be, but often times it is not. So we don't want to just throw a solenoid, or in some cases a new Transmission Control Module (TCM), with all new solenoids at this transmission just to see if it sticks and solves the problem.

Are these codes electrical in nature? Usually not, as the definition pertains to a mechanical problem. But there are a few exceptions, specifically with solenoids that have valve trains or pintle pins at the end of them that are not serviceable. If they are stuck, the solenoid will have to be replaced. Caution: If there is a solenoid circuit fault, such as a solenoid short to power, a solenoid open circuit or a solenoid short to ground code that is accompanying a solenoid performance code, we need to fix this first. After all, if the solenoid electrical integrity is faulty, we can’t expect that the solenoid is going to function mechanically. Scan tool PIDs can help you diagnose an issue with an electrical problem with a solenoid. Many pressure control type solenoids will commonly have a desired amperage and an actual amperage which will typically mirror each other when operating correctly.

Figure 3

The main components that control modules monitor to know whether a solenoid is performing mechanically in the correct manner are the Input/Turbine Speed Sensor, the Output Speed Sensor and, in some vehicle applications, Vehicle Speed Signal (Figure 1). These speed sensors provide information to the control module to determine gear ratio. The turbine sensor also is monitored during the engagement process when selecting a Drive or Reverse application. Most turbine sensors will register a little below engine rpm in Park then drop to zero when a Drive or Reverse engagement has been selected. Some control modules monitor pressure switches along with gear ratio information determined by the turbine and output speed sensors.

Pressure switch status gives information to the control module on the positioning of a particular control valve. The control module monitors a High or Low, which can also be shown as an Open or Closed position of the pressure switch. The control module provides a 5- or 10-to-12-volt signal to each pressure switch waiting for the switch to provide a ground path to the ”Switch Voltage,” which in turn provides the High or Low input to the control module. A High/Open switch equals 5 or 10-12 volts. A Low or Closed switch equals a grounded or 0.01 voltage reading when probing the wire to ground.

Figure 4

Also we need to point out that only a scan tool can monitor these pressure switches if the transmission has an internal Transmission Control Module (Figure 2).  Pressure switch information indicates that the solenoid is mechanically operating right, by valve position, when compared to gear ratio.  So as you can see there is some important information to be retrieved from the scan tool as well as information to be pried from the customer or the center manager, especially if the trouble code is intermittent.

The main point is to look at the trouble code definition, the complaint with the vehicle, then make a plan of attack based on a logical conclusion formed from fact. In many cases this can be figured out quickly, if we are familiar with the components that the control module is monitoring. Our focus should be making common sense out of the trouble code and the complaint and their relationship. I have found that if you can make sense out of a diagnosis, it will come to an end earlier than later. Dale England used to always say, “When you think you have come to a conclusion, keep asking why, until there are no more whys.” Honestly the first time he said that to me, all I could think about was the incessant questions of “why this?” and “why that?” from a 3-year-old kid. 

Following the Flow (Chart)
I like to look at problems and make a mental flow chart of what to do first, second and so on down the list. If you have been in the repair business for a long time, you remember the old flow charts with the large block at the top of the page with text inside of it and arrows to point you in the direction of the solution. The beginning of the flow chart would have the code definition, and below it would list an action, as in ohm test terminals X and Y and see if they equal XX ohms. If yes, then follow the arrow down to the next block; if no, then follow the arrow to the block on the right and perform the action based on the instructions in that box.

Figure 5

Let’s look at a 6L80 transmission and diagnose a solenoid performance trouble code looking at all of the components and criteria that the control module is monitoring for the trouble code and complaint using a simple flow chart of sorts so we can come to a conclusion that will make sense to repair the vehicle.

The vehicle is a 2007 model 2500 Series Chevy truck with a 6L80 transmission. The complaint is a flared 2-3 up-shift and a slight delay in Reverse when cold followed by a P0776 “Clutch Pressure Control Solenoid 2 stuck OFF” trouble code. The top box in our flow chart is now filled in with the complaint and the trouble code. The box below this consists of a question: Is there anything common to the complaint of 3rd gear and Reverse? If you reference the ATSG application chart as shown in Figure 3, you will see that the 3-5-Reverse Clutch is common to both complaints. The box below that is filled with what is the relationship between the P0776 and the 3-5-Reverse Clutch. Refer to Figure 4 and you will see that CPC S2 controls the 3-5-R Clutch Regulator and Boost valve. This partial oil circuit diagram shows that as the CPC S2 Solenoid is controlled, pressure to the 3-5-Reverse Clutch Regulator valve is high, which moves the valve to the right opening a passage which connects 3-5-R supply to 3-5-R feed. At the same time, notice that the passage to Pressure Switch 1 is exhausted. Refer to Figure 5 and note in the Pressure Switch logic chart that Pressure Switch 1 indicates a “0” in 3rd, 5th and Reverse, as it is exhausted as shown in the partial circuit diagram.

Figure 6

Now that we are familiar with the components that the TCM is monitoring, we can drive this vehicle and monitor these items. During the road test, we can see that Pressure Switch 1 is correlating with the chart and we have noted that the ratio in 3rd gear is 1.53, which is correct according to the application chart provided in Figure 3. During this road test we find that the 2-3 up-shift is quite flared and getting worse. The plan of action at this point is easy, because we know that the solenoid is doing its job, proven by the pressure switch logic chart, which proves that the 3-5-Reverse regulator valve is in the right position and we know that the ratio is correct. It just takes a while to complete the shift.

GM has a feature that can give us information related to the amount of time it takes to make a shift transition. Using a scan tool, we can monitor shift times and compare them to each other. In this situation, you may notice that the 2-3 and 4-5 shift time are a bit higher than the other shift times, nearing .70 second, which is close to a full second. This time equals a flared shift. With the shift time information being high, I am headed to the 3-5-Reverse Clutch inside of the transmission.

Figure 7

The point of all of this is that the TCM is blaming the 3-5-Reverse Solenoid for the flared shift as it controls the apply of the 3-5-Reverse Clutch. The problem is that many techs have gone in the direction of replacing the TCM, as the solenoids are not sold separately (see Figure 6), to find they flushed some coin right down the drain. The problem is still there after all of that work, not to mention the TCM will need to be programmed as well. Could the solenoid be mechanically faulty causing a slow fill? Yes, it could but we have information related to an update on the pump cover assembly that has been successful in repairing this issue.

The new pump cover assembly with the new style non rotational sealing rings, as shown in Figures 7 and 8 have O-ring expanders below them that prevent the rings from leaking. This update should be performed during overhaul.  ATSG Technical Service Bulletin 13-17 provides part numbers and 

Figure 8

illustrations related to this update. While we are in this area, we have also run into problems along the weld in the 3-5-Reverse clutch drum leaking, which can cause a similar complaint although it is usually related to a no Reverse complaint hot, as this weld creates a serious leak when it is at high temperature. ATSG Technical Service Bulletin 12-11 shows information on air testing the drum to find the crack and provides part numbers for a new drum.

I hope this information will help with your next solenoid performance code diagnosis, as they can be confusing, but once you break everything down and make sense out of it, you can answer the question as to whether it is an external or internal problem requiring a major repair. Information on how something works is key to fixing it the first time!

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About the Author

Jim Dial | Contributor

Jim Dial is senior technical consultant at ATSG. He has been in the transmission repair industry for 30-plus years as a shop owner and operator, and at ATSG since 1994. In 2000, Jim developed a new type of manual referred to as Technicians Guides. 

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