Wednesday, February 20, 2013

Dodge RAM:Transmission Will Not Downshift

Transmission will not Downshift to 1st gear  

transmission

Its 2001 Dodge Ram, vehicle starts and runs fine,but while slowing sown it will not downshift from second to 1st gear to make a stop.It normally gives problem when engine is hot.

Manually shift to D1, D2 and D and the transmission operates normally.

Local mechanic suggested faulty Throttle position sensor which is already been replaced with brand new OEM part,but still same problem.


EXPERT'S ADVISE:

As per problem mentioned it seems like  1-2 shift valve in the valve body is staying in the second gear position rather than returning to the first gear position when you come to a stop. So its not downshifting to 1st gear.

So first possibility is valve body issue. 

Reasons:--- 
  • Valve is physically sticking in the bore because of bore or valve damage.
  • Or its debris in the valve causing it.
  • Sometimes valves in a valve body will start to hang up more when hot which may explain why yours seems to only act up hot.

The most common thing to cause this is Governor pressure:  
  • Governor pressure staying too high  from its actual level. 
  • On the right side of the valve body is the governor solenoid and transducer which are used to control governor pressure. 
  • Governor pressure acts against one side of the shift valves in the valve body to control up and downshift timing. 
May be that required pressure is not there.

Dodge  Van Shifting Problems
HOW EXACTLY GOVERNOR PRESSURE IS CREATED?

This is all done by solenoid.The solenoid is used to control line pressure flow into the governor circuit to create more or less pressure, the transducer is the engine controller's feedback so it knows how much pressure is in the circuit.

Mostly in your case problem seems governor pressure transducer:

What usually causes your problem is a bad governor pressure transducer. What will happen is they start to report a lower pressure than actual. So vehicle has downshift issue.On your case its related 1st gear.but this problem can vary,it can be second gear issue.You never know,but all seems to be related to governor pressure transducer.

HOW EXACTLY VEHICLE DOWN SHIFT PROCEDURE WORKS?

Governor pressure should be 0 when you are stopped and build at a rate of about 1 PSI for every MPH you are traveling. 
Now if governor pressure stays up when you come to a stop then it will still be acting on one side of the shift valves, there will be no throttle pressure on the other side of the valves to counteract it, and it hangs in second or sometimes third gear when you come to a stop. So it will not set in correct gears.


When the transducer starts to report incorrect pressures the engine controller will think pressure is at 0 when you come to a stop, but actual pressure will still be high enough to hold the shift valve over.And in your case it wil not get to 1st gear and still stuck up in 2nd gear


HOW TO CONFIRM THE FAULT WITH GOVERNOR PRESSURE?

You can get the issue confirmed by watching governor pressure on a scan tool and comparing it to pressure shown on a manual gauge, but if you don't have a scan tool available then its suggested to just replace the transducer.


BUT WHERE IS TRANSDUCER?

It's easy to replace and mounted just to the right of the filter on the right side of the valve body, it takes around an hour to replace. Majority of the time this will take care of the problem you are having, and if you're looking to avoid a shop I would recommend replacing the transducer.

It can be easily replaced with basic auto repair tool kit,yes that is must.

But please make sure you buy branded auto parts,as compared to third grade low quality cheap aftermarket parts.

WHAT IS PART NUMBER FOR TRANSDUCER?

The current part number is 68164850AA and it runs for approx $100 at a dealer. The other good option is you can order it from moparonlineparts.com and get the same Mopar part for $65 and save a few dollars.

This details will help.
Thanks.


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