Code 56?
Thread Starter
Pro
Joined: Mar 1999
Posts: 666
Likes: 1
From: Wisconsin
Code 56?
I had a check engine light come on today. The reason was a code 56 - something to do with secondary vacuum I think.
Does anyone know exactly what code 56 is and how to fix it?
Thanks!!
David
Does anyone know exactly what code 56 is and how to fix it?
Thanks!!
David
Team Owner
Joined: Jul 2002
Posts: 37,017
Likes: 68
From: This city NEVER sleeps! Frank's back yard!
Re: Code 56? (C56spd)
I JUST got my helms manual for my car - is yours a '90? If so, then I'll look this one up and repost - if not, I also have a manual for 91 - is it by chance a 91? Maybe the code is the same -I'll look it up for ya. :seeya
Drifting
Joined: Dec 2001
Posts: 1,560
Likes: 4
From: Dallas Texas
Re: Code 56? (C56spd)
code 56": Port throttle valve sensor"...Circuit description: A vacuum differential sensor is mounted beneth the ECM. The purpose of the sensor is to monitor vacuum presence in the secondary port throttle actuators. This will read normally .56 volts, no vacuum present. twenty inches of vacuum will read approximately 4.60 volts.
Causes : 1. an open circuit 452 sensor logic
2. Pinched vacuum hose to sensor .
This is from the LT5 Fuel and Emissions book from STG
hope it helps some;; :cheers:
[Modified by White 68, 9:13 PM 5/3/2003]
Causes : 1. an open circuit 452 sensor logic
2. Pinched vacuum hose to sensor .
This is from the LT5 Fuel and Emissions book from STG
hope it helps some;; :cheers:
[Modified by White 68, 9:13 PM 5/3/2003]
Thread Starter
Pro
Joined: Mar 1999
Posts: 666
Likes: 1
From: Wisconsin
Re: Code 56? (White 68)
White,
I have a 95, is the code the same as all other years? I heard the sensor is mounted under the ECM on the 94's but may have been moved for 95. Do you know?
Thanks
I have a 95, is the code the same as all other years? I heard the sensor is mounted under the ECM on the 94's but may have been moved for 95. Do you know?
Thanks
Team Owner
Joined: Jul 2002
Posts: 37,017
Likes: 68
From: This city NEVER sleeps! Frank's back yard!
Re: Code 56? (C56spd)
Code 56 will be set when:
1. Vacuum sensor signal voltage is less than .46 volt at any time
2. Vacuum sensor signal voltage is greater than 5 volts at any time
This checks to see if there is a constant vacuum signal on the sensor at idle.
If the ECM recognizes the low vacuum signal, the ECM and wiring are OK.
If the ECM recognizes the high vacuum signal, the ECM and wiring are OK.
Bottom line: you need to check things with a Tech 1 diagnostic computer "scan" tool. It'll display vacuum in volts. If the vacuum sensor voltage is within spec. at idle, the code 56 may have been set when the ECM commmanded the secondary port throttle valves "ON". This refers to the fact that the necessary vacuum wasn't present to fully operate the secondary port throttle valve system. This can mean that you have a crack in one or many of the vacuum lines/fittings, or maybe something has come apart. It could also mean that your electric vacuum pump is not operational, and thus at WOT, when engine vacuum is low, the code 56 is set.
Hope this helps.
:seeya
BTW - when was the code set - at idle, or WOT?
[Modified by DDSLT5, 1:20 PM 5/4/2003]
1. Vacuum sensor signal voltage is less than .46 volt at any time
2. Vacuum sensor signal voltage is greater than 5 volts at any time
This checks to see if there is a constant vacuum signal on the sensor at idle.
If the ECM recognizes the low vacuum signal, the ECM and wiring are OK.
If the ECM recognizes the high vacuum signal, the ECM and wiring are OK.
Bottom line: you need to check things with a Tech 1 diagnostic computer "scan" tool. It'll display vacuum in volts. If the vacuum sensor voltage is within spec. at idle, the code 56 may have been set when the ECM commmanded the secondary port throttle valves "ON". This refers to the fact that the necessary vacuum wasn't present to fully operate the secondary port throttle valve system. This can mean that you have a crack in one or many of the vacuum lines/fittings, or maybe something has come apart. It could also mean that your electric vacuum pump is not operational, and thus at WOT, when engine vacuum is low, the code 56 is set.
Hope this helps.
:seeya
BTW - when was the code set - at idle, or WOT?
[Modified by DDSLT5, 1:20 PM 5/4/2003]
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