Mechanics

PONTIAC SUNFIRE TRANSMISSION PROBLEM

1996 Pontiac Sunfire • 155,000 miles

Driving down the highway, Cruise control will only sometimes engage in 5th gear, downshift into fourth maintain speed cruise will work every time. Hooked the Snap On scanner up to monitor the cruise module, in 5th gear it flashes yes/no rapidly under cruise enabled and constant no under cruise engaged. Downshift into fourth the cruise enabled stays a constant yes. Then hit the set button cruise engaged says yes, and it maintains speed. What could be causing this problem?

Cruise Servo/Module has been swapped for another and switch on column has also been changed. Holding back on VSS until I can better narrow down the root cause. Tech2 Scan tool does not display pulses per mile information and says exactly as Snap on Scan tool says Wiring to speed sensor has 5v reference

cruise also will stay engaged for 3rd gear

when engage in 5th gear it might stay engaged for seconds or a mile and when it disengages it drops gas pedal abruptly not like when you turn off cruise normally in gear

Car is a 5 speed Pontiac Sunfire GT with a 2.4 liter engine. Transmission is rebuilt and this problem happened before trans was rebuilt.
Avatar
Batterup
January 22, 2013.




All emission systems test are complete and there is no check engine light and no stored codes. I have very smooth readout on TPS sensor from 0% to 100%


Tiny
Batterup
Jan 22, 2013.
The only info I can up with is that it has to have the correct tps voltage, brake light switch open, vss constant.

OPERATION
The module will interpret the position of the servo, the position of the control switches and the output of the speed sensor. In response to these inputs, the module electrically signals the opening or closing of the vent and vacuum solenoid valves in the servo.

The module is mounted on the dash support bracket at the right side of the steering column, but is integral with the ECM on some models with certain engines.

I see no way to test with module without replacing it.

Roy


ASEMaster6371
Jan 22, 2013.
There is actually a cruise tester box you use for diagnoses that's plugs in between the cruise model and the harness that plugs into the cruise model. They sell the boxes on eBay used for pretty cheap. The box lights up on all the cruise input States. Some of the boxes actually allow you test the cruise control in the shop by stimulating vechile speed.


Saturntech9
Jan 22, 2013.
In reply to Roy

thanks for your quick help, I do not believe there is any vacuum within the cruise control system at all unless its reading the MAP sensor. When you say change the module do you mean the module that has actually pulls the throttle plate with the cable or is there another component like you said inside next to steering column that I overlooked. Or do you you mean replace the entire PCM/ECM

the brake light switch I would rule out since I do not hit the brakes at all between 3rd and 4th which cruise will stay engaged as long as id like it to in those gears. There is no information from this transmission to the pcm on which gear im in other than relative RPMS to MPH. The only 2 plugs on the trans is VSS and reverse switch its very basic. The VSS wiring has a new pigtail also

In response to Saturntech9
is the KENT-MOORE J-42958 the one I should shoot for? If that is the right one it could be used into the 2000s because the somewhat newer obii cars still have the same style cruise servo

thank you for the replies still need a little more information


Tiny
Batterup
Jan 22, 2013.
I will look up if that is the correct tool number when I get home.I am out of town right now and will be back in town sometime today. The cruise box tools are the best ways to trouble shoot cruise problems I have used them many times with great success.


Saturntech9
Jan 22, 2013.
I couldnt find any mention of a cruise module box for testing in my mitchel ondemand it tells me about using apin out test and using the tech1 scan tool to run a service bay test.I posted all the cars your cruise module fits.


Saturntech9
Jan 23, 2013.
This car does not have a tech 1 port it has OBD II port for emissions.I also own a 1995 it also has an OBD II port and does not have an OBD II computer. So I will have to use the Tech 2 and try what you recommend. The part number you posted I have replaced already with another DELCO Servo with the exact same results, also with the switch on the column.

Do we no longer think that this cruise tester will work it seems like it has all of the correct pins and connections neccessary and it was used and created in the correct era for this vehicle

im thinking there is interference with the VSS either with shavings from the last transmission or in the wiring.


Tiny
Batterup
Jan 23, 2013.
The tech 1 is a gm scan tool used before the tech 2 came out it was used on obd 2 cars. It is possible that cruise tester may work I am just saying from the info on Mitchell on demand it doesn't list a cruise tester. You maybe correct about the vss signal/sensor or shavings.I was wondering if it thinks the transmission is slipping or vss signal gets lost long enough to disable the cruise control.


Saturntech9
Jan 23, 2013.
Thanks for the reply, I will find out tomorrow if my uncles tech 1 scan tool will hook up to this car. He uses it on his Formula Trans Am 1991 so its definitely a Tech 1.

Some other miscellaneous information is this problem seemed to have happened right as the synchronizers for 2nd and 4th were lost on a long road trip not sure of the cause on that one but have a new rebuilt transmission the only common denominator is the VSS as its the only information output this transmission has. The leads look like they are exposed right as they go to the connector from the coil inside the sensor (attached pic). Upon taking it out of the bad transmission one can only imagine how many shavings were attached I was pretty shocked. Blew it out with an air gun but was nervous about the micro sized gauge wire for the signal so I didnt want to blow a lot of air close up or try to scrub the sensor.

Upon installation of the new transmission clutch and flywheel everything is perfect except for the cruise problem which happened on the road trip originally. When engaged in 4th gear now it will resume, set, accelerate, and coast as normal but I dont recall testing at 75mph in 4th gear, like I attempt to set and accelerate in 5th gear will have to try that, maybe the pulses per mile are harder to pick up, compared to going 45 or 50 when not on the interstate when I road test 4th gear.

Thank you for your response I hope to follow up with any outcome as this has been going on since October and has really tested my skills. Have never encountered anything like this.

I still wonder if its a good investment to have the cruise module tester box as you are right about them being cheap thank you saturn for your input you are the most help of any of my colleagues of techs so far


Tiny
Batterup
Jan 23, 2013.
As long as his tech 1 has the odb2 set up with the correct cartridge. So that's not the oringal transmission? What year did that transmission car and model did it come out of?Is there a vin number on the transmission?
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Saturntech9
Jan 23, 2013.

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