A quick update and a couple of questions.
1. The computer is throwing a couple of error codes:
#29 Vehicle Speed Sensor problem – VSS
#67 Intermittent Park Neutral Position (PNP) sensor fault – PNP | Transmission Manual Lever Position (MLP) sensor circuit – Transmissions | Park/Neutral circuit fault – PNP
2. The shop has a machine called "trans-x". I am not familiar with this equipment but from what i understand it sits between the transmission and PCM
. This machine can also take over PCM
. According to the mechanic the transmission behaves properly when this machine is connected. They also said they can see that the PCM
is not sending the signal to downshift.
3. The mechanic indicated that he was not getting a reading from the VSS
test port. This port is located in the front driver side compartment(by the headlight) by the EEC IV test port. As a test the mechanic ran a jumper from the VSS
(in the rear diff) to the vss
test port. The transmission shifts up and down the gears properly approximately 5 times. After 5 times the failures to downshift reappear...
4. The VSS
sensor and MLPS sensor has been replaced. Also the speedometer seems to be working fine.
All of the symptoms seem to point towards an electrical or PCM
issue. Whats driving me nuts is that this downshifting issue was not present prior to the rebuild.
???Is there any data that is sent from the transmission to the PCN that influences when it should downshift??? If so, what components are responsible?
I was going to head down to the shop and see if there is a way to test the VSS
signal at the PCN. I found some wiring diagrams that indicate that pin 3 and 6 are the VSS
. How would you suggest tapping into these connections? The test procedure I have suggests a breakout box(T83L-50-EEC-IV) while driving however I don't have this equipment.