Renix AW4 Not shifting while TCU is connected

87 xj
Trans shifts manually fine.
I swapped in another TCU and it doesn't work.

Was going to check the OSS first but can't find out how to test it.

Check the fuse under the pass side kickpanel?
Its likely covered in tape onto the harness

uglyrenixxj said:

Check the fuse under the pass side kickpanel?
Its likely covered in tape onto the harness

Click to expand...

Always worth checking that as it's a common problem. If the fuse holder is burnt, replace it with a couple of spade connectors.



So you're saying it stays in 1st gear if the TCU is plugged in, but you can shift manually with the shifter if it's not plugged in? The output speed sensor would be the first thing I check as well. That sensor in a 87 is a magnetic relay that closes once per revolution. If you measure the voltage across it with it hooked up you'll see 12 volts dropping to zero one per revolution. Or disconnected, you'll see it go to a dead short once a revolution. Stick your meter on there, trans in neutral, jack up and slowly spin a rear tire while watching the sensor.


The other possibility is a bad shift solenoid. Does it eventually upshift from first into third? That would make me lean towards a bad shift solenoid. A quick test is to check their resistance, which as I recall should be around 11-15 ohms?

lawsoncl said:

So you're saying it stays in 1st gear if the TCU is plugged in, but you can shift manually with the shifter if it's not plugged in?

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Yeah.

Oh Lol I didn't know there was a fuse there, Pretty sure I know where you're talking about. Yellow wire that goes to the TCU that goes into a loop?

I Put my tcase in neutral and trans in gear I got 0 voltage from the oss wire at the TCU.

depending on whether you have the TCU plugged in while doing that OSS test, and whether the TCU even has power, that test could mean a failed OSS or a perfectly good one. If you disconnect the TCU and run a test light from 12V to the OSS sensor pin it should blink momentarily once per driveshaft revolution on 97 and earlier AW4s. If it stays off continuously or on continuously you have harness damage, bad OSS, or the magnet fell off the reluctor wheel on the trans output shaft.

This might be as easy as changing the filter and replacing the fluid.



I bought my '90 XJ after it had sat outside for 2 years and had been worked really hard before that. The PO told me that the transmission had an issue and that it would only shift manually (along with a big long list of everything else that didn't work). The first step in my diags was to drop the pan on the transmission and what I found was that the filter was filled with crap and the fluid was black. I replaced the filter and changed the fluid (twice to get as much out of the torque converter as possible) and it has run flawlessly ever since.


HTH
Todd

kastein said:

depending on whether you have the TCU plugged in while doing that OSS test, and whether the TCU even has power, that test could mean a failed OSS or a perfectly good one. If you disconnect the TCU and run a test light from 12V to the OSS sensor pin it should blink momentarily once per driveshaft revolution on 97 and earlier AW4s. If it stays off continuously or on continuously you have harness damage, bad OSS, or the magnet fell off the reluctor wheel on the trans output shaft.

Click to expand...

Thanks for the proper test procedure!!!

tjmotter said:

This might be as easy as changing the filter and replacing the fluid.

Click to expand...

probably has 100 miles on its filter/fluid.

It could be a lack of power to the TCU, lack of ground to the shifting solenoids (Attached to the valve body) that the TCU operates to shift, or #1 and #2 solenoids are bad too?

AIbandit said:

Thanks for the proper test procedure!!!



probably has 100 miles on its filter/fluid.

Click to expand...