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My second AW4, TCM thread

bigalpha

bigalpha

Moderator
Location
Tucson, AZ
This is my DVM
So, I tested my TCM again, according to the Shift Pointers document.

C9 is 0V with Key On, in D.
C14 reads 0.F -- I get this reading at the firewall connector too.
C15 reads 13.5 ohms -- I get this reading at the firewall connector too.
C16 reads 0.F -- I get this reading at the firewall connector too.
According to the user's manual, "0.F" is when the measured value exceeds range.


My DVM has a 'short' tester to test a short in a circuit.
From D7 to D3, D16, C10, C15 all read "short". All other pins are "open".

Now, my few questions:
1. What tells the TCM that the gear selector is in D?
2. Why did D7 to C15 short, when C15 read proper ohms?
3. How do I test the Speed Sensor?
 
It controls the transmission electronically. On my rig, it's located behind the kick panel on the passenger side.
 
98 jeepjeep said:
where is the tcm and what is it?
Click to expand...

See the other thread. You don't have a bad TCM (transmission control module).

98 bigalpha said:
Now, my few questions:
1. What tells the TCM that the gear selector is in D?
2. Why did D7 to C15 short, when C15 read proper ohms?
3. How do I test the Speed Sensor?
Click to expand...

The signal on C9 comes from the NSS neutral safety sensor, when the shifter is in (D). If you don't checkout http://www.go.jeep-xj.info/HowtoNSSrebuild.htm.

Your meter probably beeps when its sees low resistance and 13.5 ohms is probably low enough. Stick with the resistance settings. The measurements on C14 and C16 would indicate an open circuit. Next step is dropping the transmission pan and measuring the solenoids directly.

The speed sensor is a magnetic switch that closes once per revolution. Try putting the xfer case in neutral and the tranny in gear with the engine running. With the wiring all plugged in, back probe pin C3 and you should see an a/c signal. BTW, turn the engine off before you try to put it back in park.
 
Dang. Can the NSS be bad enough to cause TCM problems without causing any other problems? I can only start in P and N, and I have reverse lights. I've never had NSS-related issues.

You are right about the continuity setting. It indicates 'short' under 50 ohms. Curious that it didn't do it to all three solenoid pins, though. To test the continuity of a circuit using ohms, the meter should read 'infinite' and not read any kind of numeric value, right?

I'll try that with the Speed Sensor tomorrow. I'd like to validate that it's working properly.

I assume that a bad NSS or Speed Sensor can cause tranny issues, is this the case?

At any rate, I've got something else messed up besides that, since D14 and D16 don't measure any resistance.
 
I have seen some reports of a bad NSS causing the t/c to not lockup. The usual symptom of a bad speed sensor is the tranny never upshifts because it doesn't hink you're moving. I don't know your particular meter, but a sounds like OF means infinite resistance or no connection. I agree that the D14 and D16 solenoids or their wiring are suspect.
 
lol i know everyone's name thats posted on it so far, from going over it so much.
You definitely have helped out alot!!!
I think in the end it should be a sticky.
 
scullyxscully said:
hmmmm. how should a speed sensor be tested in a 2wd?
Click to expand...

lawsoncl said:
The speed sensor is a magnetic switch that closes once per revolution. Try putting the xfer case in neutral and the tranny in gear with the engine running. With the wiring all plugged in, back probe pin C3 and you should see an a/c signal. BTW, turn the engine off before you try to put it back in park.
Click to expand...


Get a helper to very, very slowly roll forward while you probe the TCM. Or, disconnect your DS.
 
bigalpha said:
To test the continuity of a circuit using ohms, the meter should read 'infinite' and not read any kind of numeric value, right?
Click to expand...

Infinite resistance means no continuity. Continuity will mean no or low resistance normally. My Amprobe only chirps below a few Ohms (continuity check is in the <200 Ohms range, the lowest setting on the meter.)
 
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