2001 Auto Trans issues (again)

A few months ago my spedo was locked at 20 mph and the transmission locked in second. When the gas was stepped on, it seemed to go into neutral and rev way up.

Took it to shop, they found some plunger that was stuck and failed O rings.

That was fixed, spedo then sat at 0 but it shifted okay.

Yesterday the spedo went back to 20 and the shifting problem returned. As I recall there is some speed sensor gizmo in the rear diff that controls the spedo as well as all other odometer, Mpg, dte etc.

Did my shop miss the real cause ?

 

Your speedo is driven by the abs sensor on the rear diff. It could be a dirty connection or the sensor isn't fully seated. It has nothing to do with the transmission on 2001 vehicles.

Start by making sure the fluid level is correct.

You can read the PCM codes with the key in the ignition: ON-OFF-ON-OFF-ON and read the codes as the appear on the odometer. P codes are from the PCM. I think the stuck in second is limp mode when an internal sensor has failed.

 

RD, thanks ! Fluid level is perfect. The code is P PCU

So what needs to be done to fix it ?

 

It should show several codes (one every 3 - 5 seconds).
On my '02:

P PCU (indicates it's checking the power train control unit)
------ (indicates no codes present but will cycle through all the stored codes)
P donE (indicates no more codes)
------
P ECU (indicates it's checking the engine control unit)
------ (indicates no codes present but will cycle through all the stored codes)
P donE (indicates no more codes)

If you get some codes you can check the list here.

 

Got:
500 vehicle speed sensor
720 output speed sensor
1637 generator L terminal circuit

Do any of these have anything to do with my transmission problem ?

 

The 500 error relates to the ABS/speed sensor on the rear diff.
The 720 error could be your problem. It's on the transmission.
SPEED SENSOR
DESCRIPTION
The speed sensor is located in the overdrive gear case. The sensor is positioned over the park gear and monitors transmission output shaft rotating speed.
OPERATION
Speed sensor signals are triggered by the park gear lugs as they rotate past the sensor pickup face. Input signals from the sensor are sent to the transmission control module for processing. Signals from this sensor are shared with the powertrain control module

The 1637 error is about the alternator. The PCU isn't receiving a correct electrical signal from the alternator.

With sensors it's always best to start with the connectors. Make sure the contacts are clean and the connector is seated properly. Look for frayed or exposed wires.

 

Try removing the abs sensor on top of diff and clean it with brake cleaner or the like. Mine was caked with schmutz and afterwards speedo worked correctly. They're pretty cheap if you wish to replace but get from good one such as Transtsar/Transtec. MHO use quality parts...

 

The transmission speed sensor is for shifting, if that fails the PCM takes the signal from the rear ABS as last resort. If that fails also it doesn't know what to do.
Replace both Sensors and buy them OEM, i had both failing and tried Aftermarket without success, bought them twice.

 

Gentlemen, Thanks for the help.

So it seems to me that the $1000.00 the shop charged me had nothing to do with the problem ?

Pulling down he transmission, changing some O rings and plungers, pressure testing all lines was NOT the fix ?

Back when I had problems with the 3 rd , OD hunting issue that was fixed by installing that capacitor on the generator and cleaning all connections.

Sounds like more of the same and something, were it not 8 degrees, 4" of snow on the groung and my being 78 years old, is something I could have fixed myself ?

Before I "discuss" that with my shop, what do you think ?

 

I would change the two sensors before burning the bridge.

 

It sounds like they fixed one problem --"it seemed to go into neutral and rev way up" -- and caused another. If it worked for a while it could be as simple as the connector on the speed sensor (on the transmission) coming off.

The speedo is a separate issue.

 

If you have an ohmmeter the differential sensor should be 1800ish ohms and the trans. sensor 600ohms ish. That is with the sensors removed.

 

I dug out the bill from 11/3/2020

TRANSDUCER $137.00
GOVERNOR SOLENOID $132.00
GASKET $41.20
FILTER $27.85
WHEEL SPEED SENSOR $65.75
DELIVERY $12.00
LABOR 4.5 HOURS $495.00
ATF $79.90
SHOP SUPPLY $21.20
TOTAL $ 1011.90

It still does not work.

 

The Trans speed sensor isn't on the list.

 

No it is not. They do list a wheel speed sensor which I assume is the sensor in the differential but the speedo read zero which may indicate another problem like the broken wire from the frame to the axle. If that is the case I would look for the 1800ish ohms across the two pins of the sensor and if that is good a visual check of the wire.

 

Just a note on the rear speed sensor. A friend had a problem with his on his 2010 that he had a very hard time finding. This was his issue:

He replaced the connector and the sensor.

 

So they had it for 2 hours today and the tech now thinks it's an ecu wiring issue or the ecu.

Drove home in 2nd and rechecked codes.
still have:

P0720 Output Speed Sensor Circuit Malfunction

1637 generator L terminal circuit is gone although tech says alternator has nothing to do with my problem

And have a new one:
P1693 - The companion engine control module has shown a fault.

Tech got a bit pissy with me. So I STFU.

 

#1. You do not have a ECU, you do have a ECM that has nothing to do with your problem.
#2. May be a PCM issue but there are other things to check first, like wiring.
#3. I would probably stay away from that person.

 

he did say ecm.

 

Ok. ECM does like the term, Engine Control Module. What you are concerned with is powertrain thus PCM is Powertrain Control Module.
Did he ohm the speed sensor or verify it is good ?. The trans. sensor ?.