This is a for sure electrical problem. I have an 88 that all of a sudden will only shift manually. Drive equals 4th gear. Jeep couldn't diagnose in 2 hours and $106. Checked fuses to TCU and found fusible link to brake sensor burned out. Replaced and soon as I turned on key the inline (10 amp) fuse blew. Unplugged the brake sensor ( white switch at top of brake pedal) and fuse didn't blow. Are these switches known to go bad? I know it releases the torque converter when brake is applied.
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Another AW4 Problem
- Thread starter jeepgeek
- Start date
copper204
NAXJA Forum User
- Location
- Sonora, Ca
Check for proper ground on TCU plug D7.
BB1980
NAXJA Forum User
- Location
- Seneca, SC
Mine did, but it was because I had unplugged the TCU under the passenger side dash, and forgot to plug it back in.
lawsoncl
NAXJA Forum User
- Location
- North Idaho
The white switch near the top of the brake pedal is for the cruise and is also the switch that tells the TCU when the brake is applied. There is a resistor in the wiring harness up near the TCU. If that's gotten messed up and shorted you will blow the fuse when you hit the brake. Is that what you meant by a fuseable link, btw? If you replaced it with a fuse or piece of wire, then that's wha is creating a short between power and ground when you hit the brake.
Check for power to the TCU on pins D14 (red wire) and D16 (yellow wire). The yellow wire also has a fuse in the wiring harness right up next to the TCU.
Check for power to the TCU on pins D14 (red wire) and D16 (yellow wire). The yellow wire also has a fuse in the wiring harness right up next to the TCU.
- Location
- on the beach in Ocean View, VA
lawsoncl said:
X2^ that's my bet.....
The resistor wire by the TCU was no good. Just tried straight wiring it for a check and I blew the inline fuse (yellow wire by the TCU). I unplugged the switch (white one on top of brake pedal) and fuse didn't blow. Will straight wiring resistor wire cause fuse to blow? I'm going to pick one up today at parts store. Also checking grounds.
lawsoncl
NAXJA Forum User
- Location
- North Idaho
jeepgeek said:
Yes, that will short the yellow +12v wire to ground.
It's setup as a pull-up resistor. It causes the signal line to the TCU to be at +12volts until the switch at the brake pedal pulls the voltage down to ground. I don't remeber what the resistance is, but I'd guess a 10,000 ohm resistor from someplace like Radio Shack should work just fine. A two-pack of resistors is probably under a $1, or I'll mail you a couple if you need one. If you have the old one, the stripes of color around it should give the resistance. If you have a meter, try reading the resistance of the old one - it might not actually be bad?
lawsoncl
NAXJA Forum User
- Location
- North Idaho
I just measured the resistance on my 89 MJ. It measured at 1223 ohms using the el cheapo meter I keep in the glovebox. They are usually rated 5 or 10% tolerance, so a 1.5 kohm or as low as a 1.0 kohm resistor would probably work just fine. Get at least a 1/4-watt version as they'll be a little bigger and thicker leads.
RadioShack has a 5-pack for 99 cents.
http://www.radioshack.com/product/index.jsp?productId=2062324
http://www.radioshack.com/product/index.jsp?productId=2062343
RadioShack has a 5-pack for 99 cents.
http://www.radioshack.com/product/index.jsp?productId=2062324
http://www.radioshack.com/product/index.jsp?productId=2062343
OK.... Got the resistor and fuse problem fixed. Thanks, stopped at Radio Shack for resistors. I continued on checking TCU and have no power at D1 and D2 which comes from the TPS. Checked TPS and don't seem to have power at connector A. Supposed to be 5 volts. I have nothing. The Jeep starts and runs fine although idle is a little up and down. Where does the power come from for TPS? Is there a relay it goes through? Also pin C9 on TCU is suppose to have power in Drive, I don't it's in 3. I do have power at C8 when in 1-2. This is driving me crazy.
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
If you still have the C101 connector on the engine firewall above the brake booster, that is probably your problem. I cut the connector completely out and direct spliced the wires. There was a TSB on this cronic problem.
lawsoncl
NAXJA Forum User
- Location
- North Idaho
All the wiring for the TCU comes through the firewall near the TCU, and not through the C101 behind the fusebox. When you checked for power on the D1, you need to have the TCU plugged in as the TCU supplies the voltage to the TPS sensor.
This might be helpful for sorting out the wiring. You can see that D14 and D16 are the key pins to check for voltage.
http://mysite.verizon.net/~chris83803/tcu_wiring.jpg
If everything else checks out, it's possible you have a bad TCU. It's rare, but not impossible.
This might be helpful for sorting out the wiring. You can see that D14 and D16 are the key pins to check for voltage.
http://mysite.verizon.net/~chris83803/tcu_wiring.jpg
If everything else checks out, it's possible you have a bad TCU. It's rare, but not impossible.
lawsoncl
NAXJA Forum User
- Location
- North Idaho
jeepgeek said:
The diagram is a little misleading on the NSS. The detailed diagram on the TCU connector pinout calls C9 "Drive (3)". You should see voltage on D9 when its in (3), and C8 when it's in (1-2). Sounds like what you measured.
Shift Level Continuity
Position Between Terminals
----------------------------------------------------------------
Park ........................................... "B" & "C"
Reverse ....................................... "A" & "E"
Neutral ........................................ "B" & "C"
Drive ........................................... (1)
3 .............................................. "A" & "G"
1-2 ............................................ "A" & "H"
----------------------------------------------------------------
(1) - No continuity should exist between any terminals.
That's correct, I had power at C9 when in 3rd and no power in Drive. Still need to check power from/to TPS with TCU plugged in. Didn't get to it today as I was helping a friend put lift kit on his new JK. Again thanks for the info and I'll let you know about the TPS issue.
OK, the TPS is good. Ran full check on TCU and the only thing that came up was a little high ohm reading on the 3rd (TC) solenoid. Around 21 and should be 11-15. The other 2 were at 15. Dropped transmission pan and checked solenoids and all three showed 15ohms. Placed them back in tranny and checked from TCU and all showed 15 now. What gives? Could solenoid be going bad and readings change? Should I just replace all three?
