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I need some good advice on my automatic transmission. Can the output shaft speed sensor be malfunctioning without triggering codes?
Backstory: My radiator core failed dumping coolant into the trans causing error code 730, incorrect gear ratio. I had the radiator replaced and trans flushed. The car immediately provided the code again once warm and went into limp mode. At this point I should have done more research but assumed the indie Saab place I was going to knew what they were doing when they said the trans needed to be replaced. I proceeded to my friends garage and had them install a new/used trans that I sourced for half what the indie guys wanted for the install and the parts. The result is a different transmission giving me the exact same P0730 gear ratio code. There are no shift errors i.e. P0731,2,3,etc. are not coming up so the shift solenoids seem to be good. On the new transmission it will also not go into reverse without going into drive first.
Next, I replaced the trans computer still... same error (indie guys suggested this and I assumed at that point they didn't know what they were doing). So I finally say screw it and buy myself a scan tool.
The car runs as though it is confused mathematically. If I get on the throttle it spools up, quickly engages and takes off, than immediately drops the RPMs back as if the computer is saying wait a minute you can’t do that. When it decides to shift it feels mechanically sound. Once code-triggering requirements are meet for fluid temperature it goes into engine trans limp mode (not throttle body or anything of that nature). The only code I've ever gotten was the general gear ratio code. All the wiring seems to be legit. I need to do more investigation with my scan tool but it noticed while in Park the output speed went to a negative.
My understanding is that the car gets it’s speedometer information from the wheel speed sensors. The TCM uses the drive shaft output speed sensor, hence the speedometer reads fine while driving around in limp mode. I figure a wheel speed sensor would produce a different error and it doesn't feel mechanical.
What I’m wondering is the output shaft speed sensor something I can replace with some car jacks and a wrench or does the trans need to come out? Also are there relays for input (engine drive shaft) and output speed sensors that could be broken? Or do I just look for voltage or speed off the scan tool? Am I close? How good is the TCM at picking up incorrect output speed sensor values.
posted by 208.59.127...
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