Maxwell Simons

hey guys, I've got a real head scratcher here.

In August I swapped the trans on my Cherokee with a rebuilt junkyard AW4.
I ****ed up and didn't disconnect the battery and ended up grounding the starter to the chassis.

After that i got O2 sensor codes and P0720 (output shaft speed sensor circuit).
I replaced the O2 sensors and i just have the P0720 code, which ive reset many times.

I've replaced the VSS, the Output Shaft Speed sensor and Input Speed sensor with the ones from the old trans, still throwing up the code.

I've replaced the PCM and TCM(Code left until i drove it around some) then the code returned and I reverted back to the originals.

I have no idea what to look at next, any advice is appreciated.

CCKen

Here's P0720 possible causes:




P0720-OUTPUT SHAFT SPEED SENSOR ERROR


When Monitored: Continuously with the vehicle speed over 6 MPH(over the CCD bus) and the transmission is in a forward gear (1st, 2nd , 3rd orOD).


Set Condition: No signal from the Output Speed Sensor for 100seconds.


POSSIBLE CAUSES


INTERMITTENT WIRING AND/OR CONNECTORS


OUTPUT SPEED SENSOR GROUND CIRCUIT OPEN


OUTPUT SPEED SENSOR SIGNAL CIRCUIT OPEN


OSS SIGNAL CIRCUIT SHORTED TO OSS GROUND CIRCUIT


OUTPUT SPEED SENSOR GROUND CIRCUIT SHORT TO GND


OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO GROUND


OUTPUT SPEED SENSOR GROUND CIRCUIT SHORT TO VOLTAGE


OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO VOLTAGE


OUTPUT SPEED SENSOR (OUT OF RANGE)


TCM-OUTPUTSPEED SENSOR


You may want to do some testing at your TCM connector using a digital multimeter and using safety pins to probe the connector pin cavities.
Read the pin outs and test instructions carefully before beginning.
Recommend doing all the tests.

Cerveja

Did any of that help? I have a similar situation with my 2000 Cherokee Aisin AW4 Trans. I recently replaced the motor with a 4.7 Stroker, while the engine was out I sent the trans out for a rebuild because at 160,000 miles I didn't want to have to pull it a second time. Turned out it was a good idea cause the bell housing was cracked in multiple locations and needed to be replaced. When the New Bell housing, rebuilt trans and new motor were put in place, I started getting the infamous P-0720 Rear Output Speed Sensor error.


However the vehicle was driving fine in 4HI and 2HI, but in 4LO it would not shift out of first gear. The vehicle has since been back to the shop with the trans and motor in place where he did all the usual continuity checks looking for a bad wire or short to ground and found nothing. I have swapped both the input and the output speed sensor front to rear and also with a donor trans of unknown origin and the fault does not follow the sensor. My trans guy is baffled since without a rear output sensor, he thinks that the trans should not shift out of first regardless of the T-Case. I think the TCM is somehow getting a competing signal from the T-Case and using that to compensate the missing signal from the Output sensor. He thinks the TCM is going bad which is why it's still managing to shift somehow but still throwing up the fault code.


I am curious if any one has been inside these transmissions to know what the Output sensor uses to get it's signal. Is there a dedicated tone ring on the output shaft that fires the sensor or does it just run off one of the other gears inside the trans? Is it possible this tone ring was not reassembled and that is why the signal isn't present? Could the trans have been improperly reassembled that the tone ring or gear is not aligning with the sensor and thereby not activating the sensor. The shop admitted they have not done many of the AW4 Transmissions because he thinks they are very reliable units nor has he had to replace to many TCM's for the same reason. I trust the shop as they have been in business for decades and the owner is a close personal friend who I believe to be honest, knowledgeable, and quite frankly; not out to rob me or any of his customers. So I am curious what is going on with the signal and where I look to repair it next. Any input is greatly appreciated.

CCKen

See item 16. This is the gizzy that triggers the OSS.





.

CCKen

Go through the OSS test outlined above and see what yo get.

Cerveja

Alright, it was a beautiful night north of Detroit to go lay under the truck for a few hours. So I lowered the trans so I could remove the solenoid harness and inspect the wires.The OSS Pigtail was damaged and kinda melted, so I peeled back the plastic convolute and spliced in a new connecter from a donor trans and checked all the wires for continuity.W hile there, I removed, cleaned and checked the resistance from my Speed Sensors as well as the donor trans. One checked high at around 636, while the other three were all between 615-620. Iput two of the lower resistance ones back in my trans and reinstalled the solenoid harness.


As suggested, I ran the diagnostic procedure posted by CCKEN. The results are posted below. At the time of the test, thebattery voltage at the terminals was 12.21 volts. Also for section 2 items 5-7, the other test probe was back to ground as it was not specified.


Section2: Specific Resistance Checks (Ignition =OFF,Battery Neg = Disconnected, TCM = Unplugged)
1. CAV1+2 =619 ŕSpec is 620, acceptable is 500-700
2. CAV3+4 =617ŕSpec is 620, acceptable is 500-700
3. CAV4 -Not applicableŕ1997 transmissions only
4. CAV6+7 =61.3ŕSpec is 60 Ohms
5. CAV11+?24?= 21.8ŕSpec is 11-15(Solenoid C)
6. CAV12+?24?= 21.9ŕSpec is 11-15(Solenoid A)
7. CAV13+?24?= 22.0ŕSpec is 11-15(Solenoid B)


Section4: Specific Voltage Checks (Ignition = VARIED, Battery Neg =Connected, TCM = Unplugged)
1. CAV25+GRND= 12.12ŕIgnition = LOCK
2. CAV26+GRND= 11.72ŕIgnition = ON
3. CAV18+GRND= 10.56ŕIgnition = ON, Trans = REV
4. CAV22+GRBD= 11.83ŕIgnition = ON, Trans = DRIVE
5. CAV9+GRND= 11.85ŕIgnition = ON, Trans = THREE
6. CAV21+GRND= 11.87ŕIgnition =ON, Trans = ONE-TWO
7A. CAV17+16 =0.99 at IDLEŕSpec is 0.26-0.96Ignition = ON, Engine = OFF, Throttle = NotDepressed
7B. CAV17+16 =3.18 at WOTŕSpec is 4.49 or lessIgnition = ON, Engine = OFF, Throttle =WideOpen
8. CAV6+GRND= 2.43ŕSpec is 2.43
9. CAV7+GRND= 2.45ŕSpec is 2.45


Okay, so according to the numbers, my resistance on solenoids A, B & C were all a little high, not sure if that makes adifference or not. In addition, my idle voltage on my TPS was higher than spec while my Wide Open throttle was a bit low. I do not remember my exact idle rpms, but maybe it needs to be adjusted down a bit which might explain the higher than spec voltage at idle. Everything else tested good, Wiring didn’t appear damaged, Sensors,voltage and resistance for the most part all seemed reasonable. Unfortunately all tests were done with theTCM unplugged, so I am still not sure the TCM isn’t going (or gone bad). Is there any way to test the TCM itself, or should I just snag one from the junkyard and see if the problem remains? I was not able to take it for a test ride as I still need to retighten the exhaust and replace the trans crossmember. I hope that I can fire it up tomorrow, clear the code and my problem is solved. But just in case not, any thoughts or recommendations on where to go next are appreciated.

93civEJ1

Bump, any updates on this code? My CEL stays on due to this code.

CCKen

No, there's no test of the TCM you can perform. Get one from the bone yard and see if it helps.

justinswow7

Does anyone have a good description of where the G106 ground is located on the 97 Jeep GC?

lawsoncl

For future reference, the forum for the Grand Cherokees is https://www.cherokeeforum.com/f5/

Here's a great thread with pictures, showing all the ground. https://www.jeepforum.com/forum/f310...-info-4192594/