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  #1  
Old November 26th, 2013, 18:34
HappyDog HappyDog is offline
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AW-4 Shift Controller

I thought I understood how the AW4 operates, but evidently I don't.

I have two XJs, a 1997 and a 2001, each of which has an I6 engine and AW4 automatic transmission.

I put the 2001 under manual control by unplugging the TCU. When I put the shift lever on 3 I get second gear, which is what I want, and I also get engine braking, which is what I also want.

However, when I do the same thing on my 1997, I get second gear for acceleration, but NO ENGINE BRAKING!

So, is the AW4 in 1997 Cherokees different, or is the one in mine defective?

TIA!
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  #2  
Old November 27th, 2013, 07:02
O-Gauge Steamer O-Gauge Steamer is offline
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Re: AW-4 Shift Controller

With the TCM out of the circuit, the first thing that should happen is a MIL. The dreaded Check Engine Light. This should be true for both XJs.

The manual says that without the TCM, the transmission should give reverse when in the "R" TRS position, first gear in the "1-2" position and third gear in either the "D" or the "OD" positions. The torque converter will not lock up.

The '97 transmission, in the fail mode, should not provide braking, it should just overrun. So, to answer you question directly, nothing is wrong with either transmissions.

Why would you wish to attempt to operate without the TCM out of circuit? You do understand that these transmissions require the electronics, yes?
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Old November 27th, 2013, 20:07
HappyDog HappyDog is offline
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Re: AW-4 Shift Controller

Quote:
Originally Posted by O-Gauge Steamer View Post
With the TCM out of the circuit, the first thing that should happen is a MIL. The dreaded Check Engine Light. This should be true for both XJs.

Why would you wish to attempt to operate without the TCM out of circuit? You do understand that these transmissions require the electronics, yes?
I was trying to understand why the controller I built for the 2001 wasn't giving the expected results in the 1997. It seemed easiest to pull the plug on the TCU to be certain the transmission was responding only to the shift lever and not to the solenoids. I have no fear of the MIL.

Quote:
Originally Posted by O-Gauge Steamer View Post
The manual says that without the TCM, the transmission should give ... third gear in either the "D" or the "OD" positions. ....
That's not my experience. When the TCU is disconnected both the 1997 and 2001 are in second gear when the shifter is in "3." Also, the ATSG AW4 Service Information shows on page 6 that the second coast brake is active with the selector in 1-2 or 3, but not in D.

Quote:
Originally Posted by O-Gauge Steamer View Post
The '97 transmission, in the fail mode, should not provide braking, it should just overrun. So, to answer you question directly, nothing is wrong with either transmissions.
If that's so, why does the 2001 provide braking under the same conditions?
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