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lockup solenoid diagnostics
thanks to this group and its collective wisdom, i think i finally have
my lockup solenoid problem licked. a while back, in the cold weather, the lockup clutch wasn't coming on and i was worried my 89 civic auto transmission was giving up the ghost at only 155k miles. at the same time as hunting that down, i'd replaced the ecu for other reasons and got a solenoid code. once the solenoid was replaced, the code disappeared, and everything appeared to operate correctly. however, yesterday morning was a little chilly, and the lockup clutch wouldn't come on again! even after the motor appeared to be at full working temperature. i was wondering if previous efforts to fix were flawed and that this was a hydraulic pressure problem - a symptom of a weak pump, especially as this car has been abused in the past and flushed with non-honda atf. but to be absolutely certain, i decided to do one more test. thanks to this group, the archive showed people testing their solenoid operation with appropriately wired led's to show when the ecu gives signal. following this suggestion, i built a led tool to do the same thing, plugged it in and went for a test drive. the solenoid worked flawlessly each time it was getting signal, so the solenoid and the ecu were fine. but, driving with my hand on the shifter, something i don't normally do, i noticed that the /slightest/ pressure toward the d3 position, and the ecu would switch the solenoid off! conclusion: cold weather = very slight thermal shrinkage in the cable, just enough to throw an imperfectly adjusted shift position out! and that kind of component doesn't warm up as quickly being as it has no direct source of heat. anyway, that will now be re-adjusted and hopefully this problem will not recur. in the mean time, i'm driving about with a very cool led signal on the top of my dash! parts list: * 1x red led. * 1x 2.2k-ohm resistor. * wire. * appropriate ecu plug terminals cannibalized from a junkyard. method: popped the plug from the ecu, and having identified the correct wires from the workshop manual circuit diagrams, released the leads for the solenoid output and ecu earth. [a8, yellow, if you're interested.] plugged "take-off" leads back into the plug and the former ecu connectors. the led [and series resistor] is basically wired parallel to the solenoid from these two leads. appropriate shielding to prevent accidents and taping wires into position, and you're in business! again, thanks to the group for this little nugget - saved me a lot of money on mis-diagnosis and transmission replacement. |
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#2
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lockup solenoid diagnostics
jim beam wrote:
> thanks to this group and its collective wisdom, i think i finally have > my lockup solenoid problem licked. a while back, in the cold weather, > the lockup clutch wasn't coming on and i was worried my 89 civic auto > transmission was giving up the ghost at only 155k miles. at the same > time as hunting that down, i'd replaced the ecu for other reasons and > got a solenoid code. once the solenoid was replaced, the code > disappeared, and everything appeared to operate correctly. however, > yesterday morning was a little chilly, and the lockup clutch wouldn't > come on again! even after the motor appeared to be at full working > temperature. i was wondering if previous efforts to fix were flawed and > that this was a hydraulic pressure problem - a symptom of a weak pump, > especially as this car has been abused in the past and flushed with > non-honda atf. but to be absolutely certain, i decided to do one more > test. > > thanks to this group, the archive showed people testing their solenoid > operation with appropriately wired led's to show when the ecu gives > signal. following this suggestion, i built a led tool to do the same > thing, plugged it in and went for a test drive. the solenoid worked > flawlessly each time it was getting signal, so the solenoid and the ecu > were fine. but, driving with my hand on the shifter, something i don't > normally do, i noticed that the /slightest/ pressure toward the d3 > position, and the ecu would switch the solenoid off! > > conclusion: > cold weather = very slight thermal shrinkage in the cable, just enough > to throw an imperfectly adjusted shift position out! and that kind of > component doesn't warm up as quickly being as it has no direct source of > heat. anyway, that will now be re-adjusted and hopefully this problem > will not recur. in the mean time, i'm driving about with a very cool > led signal on the top of my dash! > > parts list: > * 1x red led. > * 1x 2.2k-ohm resistor. > * wire. > * appropriate ecu plug terminals cannibalized from a junkyard. > > method: > popped the plug from the ecu, and having identified the correct wires > from the workshop manual circuit diagrams, released the leads for the > solenoid output and ecu earth. [a8, yellow, if you're interested.] > plugged "take-off" leads back into the plug and the former ecu > connectors. the led [and series resistor] is basically wired parallel > to the solenoid from these two leads. appropriate shielding to prevent > accidents and taping wires into position, and you're in business! > > again, thanks to the group for this little nugget - saved me a lot of > money on mis-diagnosis and transmission replacement. followup for the archive: it wasn't the selector switch, it was simply the thermostat. didn't expect that - i'd put in a new honda thermostat last year, but this one gave up the ghost early. new thermostat, instant solution. |
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