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Solenoid tester for automatic transmissions

HT-SOL 25 Transmission Solenoid Tester


Hydra-Test SOL is a tool used for checking the condition of solenoids of various automatic transmission manufacturers. Cottingham Engineering designed a number of various solenoid test blocks making it possible to run tests for the majority of most popular makes on the present-day market. The unit is powered by our special version of the HTC-K Controller adapted for solenoid testing.​


Hydra-Test Solenoid Test tool from our company now comes in one universal model that covers any Customer’s preference in transmission rebuilding operations: 


  • Single tank with improved capacity for Cold/Hot Solenoid Tests.

  • Possibility to run tests at maximally high required temperature.

  • Solenoids are tested as they operate with the valve body, using in, out and exhaust as originally designed.


Which problems does HT-SOL 25 solve?

  • Electrical failure (Open/Short or weak performing): Generally modern solenoids are electrically reliable but we compare the electrical performance against the hydraulic reaction.

  • Contamination from Debris: From our experience this is the number one reason for solenoid failure. It can cause poor flow and slow to respond performance.

  • Worn seating causing a poor seal and failure to fully close.

  • Internal seal failure.

  • Worn valve bore wear, mainly found on a Linear solenoid.

  • Bushing issues: mainly referring to Aisin Linear solenoids.

New features of Gen 4 Solenoid tester

  • Increased pump performance

  • Max test pressure increased to 360 PSI (25 bar)

  • Larger capacity easy-to-replace filter with better performance characteristics

  • Added tank drain port (for fluid change and flushing of the tank)

  • Larger heating element (Increased to 1.5 kW)

  • An additional temperature measurement has been added to the solenoid supply. Temperature of ATF is not only measured in tank, but it also where the ATF is entering the solenoid adapter block with the solenoid under test.

  • Two Emergency switches are standard on the machine. One switches off the pump and the heating element when the ATF falls below the low level, the second is an easily accessible operator-controlled Emergency Stop button.

  • The solenoid control system has the ability to start solenoid control before starting the hydraulic pump.

  • Dimensions of the machine have been increased (+4 inches in width, +2 inches in depth) for easier access and solenoid adapter replacement.

  • The machine cover panels have been improved for better access for maintenance and cleaning.

  • Interior solenoid testing area has been increased.

  • The machine has been designed to keep ATF from forming puddles in the test area.

  • A secondary heating system has been included to control the temperature of the solenoid adapter block and solenoid under test (by flooding with heated ATF at the required test temperature)

  • A dedicated shelf for the keyboard and mouse has been added to keep it off the work bench surface.

Solenoid Testing Modes

Electric test of the solenoid

The electrical continuity (open or short circuit) and resistance of the solenoid is tested by observing the values of the current consumed by it (PASS/FAIL check)

Manual mode

The solenoid is tested by manually varying the operating voltage duty cycle (0-100%) and the inlet pressure, while monitoring the current, pressure, and temperature.

Automatic mode (Scenario)

The solenoid switches automatically according to a user-defined test scenario. During the scenario, the average voltage (controlled by duty cycle), the rate at which the voltage increases or decreases with time, as well as duration of any static voltage are sequenced automatically. The user can choose a prewritten sequence (script) from the extensive library or create their own.

Automatic mode 1

Depending on the user settings, this mode partially or completely repeats the specified scenario (script) in a cyclic mode. It allows repetition indefinitely as all parameters are switched automatically. The mode is stopped by the operator. It is used for long-term solenoid testing. In this mode, it is possible to display current and pressure parameters of the solenoid in real time with overlay of the reference result from the library. Any test results (for example, “before” and “after” solenoid repair) can be used as a reference.

Automatic mode 2

This mode is similar to the mode 1. It is used when two independent parts have to be “looped” in time in the test scenario (script). For the first half Automatic mode 1 is used, for the second half – Automatic mode 2 is used. In this mode, it is possible to display the current and pressure parameters of the solenoid in real time with the overlay of the reference result from the library.

Real-time mode

It is available in all automatic test modes. Live displays of the values of the current and pressure are shown on the chart in real time.


What does HT-SOL check?


Our intention with HT-SOL is to prove the functionality of a solenoid. After many trial and experiments it was decided that if a solenoid cannot be successfully accessed and cleaned thoroughly no alternative cleaning method will recover it sufficiently to last any reasonable warranty period. "Therefore if it works good, use it, and if it doesn’t work good, replace it" became our policy.

What is the testing method employed?


Our testing method is to feed a varying current to a solenoid and check for the correct response time of both current and pressure/flow. With ON/OFF DC solenoid this is easy to achieve. However, after working with many variable solenoids we discovered that the speed of the testing operation is critical to showing a faulty performing solenoid. For example, we found that a sticking Linear Solenoid can be missed when testing if the current supplied is changed too fast. Using this experience we found an ideal speed to “ramp” a solenoid from fully off to fully on and then back again. We also noticed that some solenoids perform badly when applied and other when deactivated. For this reason all solenoids are ramped on and off during testing.

With all previous points considered we decided it was vital to build certain features into our own HTC-K Controller. Extremely fast resolution of data capture was first on the list so 100hz was replaced by 500hz.

How are HT-SOL test scenarios written?


Test script creation was a tedious and complicated process using all previous control systems so a simplified method had to be found. Instead of writing 100’s or sometimes 1000’s of lines of coding we were able to reduce this to just a few lines by adopting a Hardware/Software method we call “Linear Interpolation”.

This method allows us to take any solenoid from 0% Duty Cycle to 100% (typically 60%) Duty Cycle smoothly and precisely through 1% increments in a set time period. So instead of writing 60 lines of code this can now be achieved with one line only. Then should we need to speed up the process or slow it down, only the time period needs to be changed.

What are the benefits of having HT-SOL?


The HT-SOL was designed to accurately test solenoids at high temperature. It has a small reservoir with fast heat up from cold. The Adapter plate for HT-VBT was a low cost introduction for existing customers to understand to benefit of solenoid testing. The major downside to this method is getting high temperature to the solenoid as the cabinet is much larger and therefore any heat dissipates quickly. Almost all customers starting out with the Adapter plate follow up with a HT-SOL machine order for two reasons. The first reason as mentioned above and the second reason, most shops are busy testing valve bodies on the HT-VBT and prefer to test solenoids separately.

transmission solenoid ultrasonic cleaner

ADD-ONS: Ultrasonic Cleaner

An additional ultrasonic cleaner can be added to your HT-SOL 25 test machine to clean solenoids before you test. Cleaning them before testing will make sure your testing process is not influenced by debris and dirt of dirty solenoid. It will also keep the fluid in your machine cleaner and decrease the frequency you need to change the fluid. 




  • 5 minutes cycle with automatic shut-off

  • 35 watt ultrasonic element

  • 40 kHz ultrasonic frequency

  • Tank size (LxWxH) inches – 6.10 x 3.75 x 2.00

  • Tank capacity – 20.3 Fluid oz.

  • Solvent based liquid 

solenoid tester adapters


Hydra-Test offers an ever-increasing line of solenoid test blocks that allow you to test each solenoid hydraulically, just like it performs in the vehicle while being able to see leaks, potential wear, or other functional issues that would be impossible otherwise. Our dedicated engineering staff is continually developing new test blocks to cover the latest transmission solenoids on the market before they get to your shop. These blocks are made from precision machined aluminum to keep them light and easy to install in the machine. High quality quick connect hose connections to the machine allow for leak free and secure connections for accurate readings.

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Newest development - 0AM (DQ200)

The new 0AM valve body testing tool serves as an add-on to an existing Hydra-Test solenoid tester or VB tester running on HTC. It is driven and controlled very similarly to a standard adapter plate.


The 0AM (DQ200) tool verifies:

• Pump performance
• Pump motor degradation
• Pressure loss
• Solenoid Amperage
• External and internal leaks

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Where can I buy spare parts for Valve Body rebuilding?​

  • Restoring worn valve bores and replacing valves and solenoids require additional tools, an example being vacuum testers and reamer kits. We, at our facilities in Kettering do not rebuild Valve Bodies. Rather than compete with, we support our clients in this business. However, we do have vast experience in this specific field and we share our knowledge during training either at our facility in England or during on-site training. It is an important bonus for our customers that we offer free training with the purchase of a Valve Body testing system.

  • It is advisable to hold a small stock of spare parts for your Valve Body rebuilding business. This investment is purely depending upon your projected workshop volume. We can if required advise a customer of a minimal stock requirement for specific valve bodies.

Is it possible to test 2 (or more) solenoids with HT-SOL in one session?

  • When using our solenoid tester, we test the solenoids individually. So we would send transmission fluid into the solenoid, energise and de-energise the solenoid and then monitor the mechanical and electric performance of that solenoid. We generally mount multiple solenoids into the block where possible, but we are only checking one at a time.

  • Alternatively, if we want to monitor the solenoids simultaneously, we can test them in the valve body whilst fitted to our Valve Body Test Machine.

What to do if there is no ready unit to test certain solenoids?​

  • We currently have more than 30 Solenoid test blocks available for HT-SOL. We have a full time development department dedicated to expanding our range. Should a customer need a particular Solenoid test block that is crucial to their own business requirements, we will place it as a high priority on our ever expanding list of development projects.