Code 56?
 

Just got done putting her all back together after replacing the secondary vacuum solenoid under the plenum.

I get code 56 now. Searched and can't find any reference to it at all.

Re: Code 56?
 

http://www.troublecodes.net/GM/90_57J.shtml

Vacuum sensor voltage was either above 5 volts or below 0.46 volts.

Maybe a connector not connected?

TomC

Re: Code 56?
 

Has anyone replaced their vacuum sensor recently? This is the one under the plenum used to control the secondary throttle valves.

The new one I got from the local GM parts store looked correct except for on the connector side, there ws a third nipple for vacuum. I tested this and it was ported to the same vacuum source going to the secondary throttle valves. I just plugged this up.

Maybe these new sensors read differently?

Man I dont' want to pull the plenum again.

Re: Code 56?
 

Ok, the sensor I replaced is only a 2 wire sensor. I found my 90 FSM, and it lists Code 56 in it.

The Vacuum Sensor is a 3 wire sensor. I don't think they are referring to the MAP, but I checked it and it is connected properly.

Looking at Code 61, which also refers to the Vacuum Sensor, it does appear to not be the MAP.

So, where is this Vacuum Sensor located?

Re: Code 56?
 

Alrighty, found the Vacuum Sensor, it is the one under the ECM. When I unplugged the vacuum line, I heard it release the vacuum. So it is holding vacuum properly.

Anyone had one of these fail?

Re: Code 56?
 

Code 61 is a port throttle system failure. The ECM sees the voltage on the Differential MAP sensor (the one under the ECM) drop to below .7v. It assumes there isn't enough vacuum to hold secondaries open and shuts secondaries and injectors down. Check vacuum pump and under plenum for leaks. Sorry!:jawdrop:

Re: Code 56?
 

Update:

The Vacuum sensor was reading almost 5Vs. Somehow the port throttle vacuum soleniod, the one that controls the secondary flaps was staying open allowing the secondaries to be open all the time.

Tore the plenum down, all vacuum lines are as they should be. Tested them all. Reseated the connector on the solenoid, and then tested the vacuum sensor with my multimeter, would still read high.

Tapped the solenoid with my screw driver, released vacuum from the secondaries, and tried again, and everything works. Brand new solenoid stuck open the first time it was used.

All is well now, for the time being....