QuestionQUESTION: Servo holds vacuum but diaphragm does not move. All 3 solenoids (vacuum, vent and dump) click when grounded. My schematic shows pin 1 is vacuum, pin 2 is vent, pin 3 is 12 DC, pin 4 is dump, BUT on unit pin 1 grounded causes vacuum to dump. With pin 4 and 2 grounded and vacuum applied, the diaphragm does not move. Is the unit bad or am I testing it wrong? Thanks in advance! Robert
ANSWER: Hi Robert,
I don't have any Jeep manuals but I do have the Chrysler ones in that time frame. I can xerox copy and send you some pages that speak of two approaches: checking for fault codes using a diagnostic code reader (have you done that and gotten any codes?), and testing the system depending upon the nature of the problem. I suspect you will get to the bottom of this if you have the pages from an applicable manual. So let me know a postal mailing address and I will get those copied and in the manil.
Roland
PS Sorry for the delay in responding but I just found your question in the 'pool' to which it had been referred by Kevin. Please 'rate' my answer, and where you see the question about 'volunteer of the month' consider giving a 'yes'. Thank you
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QUESTION: Thanks so much, I will give you a great rating. I do have a schematic and working on fault code P1595 (shorted or open vent or speed control circuit). I have the servo out and now think its bad, but no sure because the solenoids seem to activate. I just can't get the diaphragm to move. If you can fax the info you have (fax )I will check it against mine. Would it be possible for me to call you? I need to get another part tomorrow if possible. Thanks again for you quick response.
AnswerHi Robert,
I have something similar to what you describe in either the '98 T&C or the 98 LH sedan manuals.
The servo is tested in a 10-step procedure as follows:
Turn the ignition switch to the On position without starting the engine. Activate speed control On switch
Disconnect the the 4-way connector and the vacuum harness at the servo
Connect a jumper wire from pin 3 of the servo to pin 3 of the connector
Ground pins 2 and 4 of the servo, do not connect pin 1
Connect a hand held vacuum pump in the vacuum nipple and apply 10-15 lbs of vacuum
If servo pulls cable replace servo
Ground pin 1 of servo
Check that throttle cable pulls in and holds as long as the vacuum pump is connected. After one minute check if cable is still holding. If cable does not hold replace servo.
Disconnect jumper from pin 3. Cable should return to rest position. If not, replace servo
Reconnect vacuum line and 4-way connector.
I am not certain how to compare that test procedure with what you are saying about the diphragm movement, but it appears to be a more dynamic approach.
I don't have a scanner or ability to fax. I do have '04-06 Chrysler and Dodge manuals on CD and an '06 Jeep manual on CD any of which I can copy pages from and email to you. I just need to know your email address. But whether these apply to your Jeep is uncertain. Yours is the first detailed inquiry I have had about the servo so I am a total amateur about it. It probably wouldn't be worth the cost of a phone call. If you want some pages as described then send me a follow-up question using the 'private' option, otherwise the site erases both email and fax addresses from what I am shown.
Roland
PS Thanks for doing the 'rating' and for considering giving a 'yes' to the question about 'volunteer of the month.
