Quality Transmission’s Self Diagnostic Aid

  1. The first thing you should do when you suspect any transmission problem is to check the transmission fluid level and condition.  The engine should be running with the transmission in “PARK.”  With Chrysler products, check level with the transmission in “NEUTRAL” with the parking brake set and engine running. Tip: Always insert the dipstick 2 or 3 times, look at both sides, and check for a consistent reading.
  2. If the fluid level is low, fill to the proper level and test drive the vehicle.  If the abnormal symptoms are gone, your primary problem is a leak.  Continue to monitor the fluid level, add as appropriate, and have the leak source diagnosed before additional problems occur.  NOTE: A slow leak is worse than a big leak!  A slow leak will allow the transmission to operate until the level is low enough to subject the unit to low fluid operation which will cause excessive wear!  A big leak will certainly get your attention and usually results in little or no internal damage.
  3. There are numerous transmission seals, gaskets, and o-rings that can leak.  Therefore, a visual inspection is necessary to determine leak sources before an estimate for repair can be made.

If the fluid level is okay, and you still have a problem…

  1. Check for any transmission related linkage, vacuum hoses, or electrical connections that may be lose or disconnected.  One of the most common problems are corroded battery terminal connections.  Clean terminals are particularly important for late model computer controlled transmissions!
  2. The following is general information regarding computer controlled transmissions:

Late model transmissions are controlled by a computer that operates shift and pressure control solenoids inside the transmission. Therefore the computer needs to be electrically scanned by a transmission professional to determine if any electronic control problems exist. When the computer “sees” any parameter from various sensors that do not fit established criteria, the computer will set a code for each error, which will be evident by a “check engine” and/or a flashing overdrive light. However, there are some errors that will be present that the computer will not sense because they are within the normal range. In that case, the system has to be diagnosed to determine if applicable sensors or other electrical components are performing incorrectly and creating an abnormal transmission operational response. The following sensors are usually part of the transmission: MPLS (Manual Linkage Position Sensor), input and output speed sensors, shift solenoids, governor sensor, etc.

Please be aware that some sensors are not part of the transmission itself, but in other areas of the vehicle. These include the TPS (Throttle Position Sensor), the MAS (Mass Airflow Sensor), MAP (Manifold Absolute Pressure sensor), PCM (Power Control Module or Computer), DSS (Differential Speed Sensor), CTS (Coolant Temperature Sensor), IAT (Intake Air Temperature), etc.

Also, be aware that a scan done at a “parts store” will not show all of the information necessary to form a conclusion about an electrical control problem.  A lot of problems in the control system do not set a code in the computer, but can still cause transmission problems.

When the shifts of a computer controlled transmission are excessively firm, the pressure regulator may set to maximum pressure by the computer if it senses a problem from one or more sensors.

The results of this diagnostic testing should indicate whether the problems are in the control system, the transmission, or both.

When the ignition key is cycled, the computer is reset and will control the transmission normally until an error is registered.  Then the transmission will be placed in “limp” mode (2nd gear) again.

I’ve found that it much better to evaluate the situation “hands-on” than to speculate on the phone. Over the years, I’ve been amazed at the number of times the conclusion made before seeing a vehicle changes after it is inspected and the situation is diagnosed.

For further diagnosis, repair, or a second opinion, look for an ATRA shop in the yellow pages under transmission. Quality Transmission Service in Tempe is an ATRA shop and we’d be happy to take a look at it for you.

Make an appointment at our facility in Tempe, AZ

Not in Tempe or the surrounding areas? Locate an ATRA shop near you.

Want access to professional diagnostic and repair information for your vehicle?

Click on the ALLDATA or Mitchell-on-Demand logo below.

  

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4 Comments

  1. Posted January 24, 2014 at 12:06 am | Permalink

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    221 South McClintock Drive
    Tempe, AZ 85281-2211
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    info@quality-trans.com
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