95 Chevy (Knock Sensor/Service Engine Soon)

I replaced the knock sensor and now the service engine soon light has come on and hasn't gone off. I should tell you that i didn't disconnect the negative battery cable before installation as the manual says. Would this have anything to do with it?

Use a paper clip to find what code (or codes) is stored. See http://www.troublecodes.net/GM/ for details on how to read the codes with a paper clip.

//2000CAYukon

Tried the paper clip but didn't get any results. I took it to a local part store to get a diagnostic test ran on it but they didn't have a scanner to hook up to it. Something about if it was a 96 model, they could do it. Although the manual doesn't say it, I'm wondering if the sensor has to be tightened to a specific torque? I know it's working because i have no more pinging in my truck. I even drove it up a steep hill to see. That service engine light is just damn aggrevating!!!!

Tried the paper clip but didn't get any results.

Can you be more specific? Did you have the ignition on but not running the engine? Did you jumper between A&B? Did the Check engine light flash at all when you did this?

//2000CAYukon

Ignition was on but not running, jumped A&B and no flash whatsoever.

Okay, i purchased a code scanner for my truck and it spit out codes: 32 and 43. According to the manual, Code 32: Barometric pressure sensor circuit failure OR EGR valve closed during start-up or open when EGR flow requested by ECM OR EGR/EVRV. Code 43: EST circuit - low voltage detected or ESC - circuit problems.

Can anyone tell where to start. I'm not sure if the EGR valve is bad or what? What i do know is, before I replaced the knock sensor, my service engine light would come on every once in a while. All i had to do was restart the truck and it would shut off. Now it's just on whenever i start the truck.

PLEASE HELP/ADVISE!!!!!!

With the engine running try to push on the diaphram in the EGR valve this should open the valve and the engine should start to sputter or idle low. If it doesn't, or the valve is stuck then you have a problem with the valve or EGR passages. The ECM will only ask for EGR flow when you are at operating temp and at cruising speeds so if the valve isn't working you will get a check engine light at those conditions. When you set timing on these older vehicles that still use a distributor to control timing, you have to go into EST bypass mode by disconnecting an electrical connector and this will set a code. Thats what that code 43 sounds like. Clearing codes on pre 96 vehicles is as simple as disconnecting the battery.

okay, thanks for the response. I will try that this weekend and post thread afterwards.

You can push the EGR to check if it stuck; however, it also has to hold vacuum to work properly. You need a vacuum pump to test the EGR. With the engine off, apply around 20 in-HG of vacuum to the EGR valve (not the solenoid). It should hold the vacuum. If not, replace the EGR valve. If it holds, start the engine. The vacuum should drop to zero, if not replace the EGR valve.

To test the solenoid, apply vacuum to the TBI side of the solenoid. It should hold vacuum, if not replace solenoid. If it holds vacuum, connect PINs A and B of the ALDL connector (see www.troublecodes.net/GM for details) with the ignition on, and the vacuum should drop to zero (note disconnect the EGR side of the solenoid for this test).

Also make sure the vacuum hoses are in good shape since a vacuum leak on either hose can set the Check Engine Light.

//2000CAYukon

Well I pushed the diaghram of the EGR valve in and the engine did sputter and idle low. However, I guess I need to vacuum test it and the solenoid to be sure. Where can I get a vacuum and is it expensive?

Well I pushed the diaghram of the EGR valve in and the engine did sputter and idle low. However, I guess I need to vacuum test it and the solenoid to be sure. Where can I get a vacuum and is it expensive?

Now you know that the EGR is not stuck. I paid around $50 for the vacuum pump at a local parts store. I use it a lot so it was worth the money to me.

Something like http://www.partsamerica.com/ProductDetail.aspx?MfrCode=PBI&MfrPartNumber=648744&CategoryCode=3412

//2000CAYukon

Okay, I'm confused a little bit and If you read further i guess you will see why. I purchased a vacuum pump attahched it to the EGR solenoid valve applying 20 in-HG and it held vacuum just fine. Here's where i get confused. In one of my previous statements, I depressed the diaphram of the EGR by hand and the engine sputtered...etc..etc. However, I connected the vacuum pump to the EGR valve and applied vacuum and nothing changed in the idling or running of the engine. How is that when I depressed the EGR valve by hand, it changed the idling of the engine. Does this mean that the EGR valve is bad?

When you connect the vacuum pump to the EGR (where the vacuum line connects), it should pump up and hold vacuum. If it doesn't the EGR diaphram has a leak, and the EGR valve will need to be replaced. As far as the knock sensor replaced without battery disconnected, don't worry about that. After you test/repair the EGR system, disconnect the battery for a couple of minutes, that SHOULD reset the check engine light and clear any codes set by diagnosing and or repairs you have done in the past. Then if the check engine light comes on again. You shouldn't have any additional codes to confuse you. Hope this helps.

I replaced the EGR valve and the service engine soon came back on after about 30 secs or so. I re-scanned the vehicle and the code 32 has been elimated which i assume the new EGR valve did that. Now I only have the code 43 which I assume has something to do with the ECM or new knock sensor. According to my repair manual, the knock should have a resistance of 100K ohm and mines is at 99.6K ohm which i guess is fine even though i dropped it by mistake before putting it on.

PLEASE ADVISE......

I replaced the EGR valve and the service engine soon came back on after about 30 secs or so. I re-scanned the vehicle and the code 32 has been elimated which i assume the new EGR valve did that. Now I only have the code 43 which I assume has something to do with the ECM or new knock sensor. According to my repair manual, the knock should have a resistance of 100K ohm and mines is at 99.6K ohm which i guess is fine even though i dropped it by mistake before putting it on.

PLEASE ADVISE......
99.6K is close enough. Did you disconnect the battery to clear the codes?? Sorry if I missed that.

I have access to online repair manuals, but I need some information about your truck. What engine is in it? How many knock sensors does it have? (1 or 2). Does it have a spark control module? There are about 6 different charts depending on the answers to those questions. Post the info, and I'll try to help.

I disconnected the battery before I started the process of installing the EGR valve and I reconnect the cable until installation was complete. However, according to my Haynes Manual, Code 43 says that the knock sensor is not getting a signal from the ESC Module. If this is true, is their any way I can test it before investing in a new one?

P.S. My engine is a 350, 5.7L, automatic. I have one knock sensor under the engine block.

I disconnected the battery before I started the process of installing the EGR valve and I reconnect the cable until installation was complete. However, according to my Haynes Manual, Code 43 says that the knock sensor is not getting a signal from the ESC Module. If this is true, is their any way I can test it before investing in a new one?

P.S. My engine is a 350, 5.7L, automatic. I have one knock sensor under the engine block.
Just a thought- it COULD be as simple as a bad connection or broken wire. I had that happen when changing a starter once.

I have the factory manuals for 1990 and I am not sure about the differences between 1990 and 1995; however, this may help.

FSM says that a code 43 is set when low voltage is seen on the ESC signal for more than 5 seconds with the engine running.

On my 90, there are 5 pins on the ESC module.

A is not used.
B is power connected to a Pink/Black wire. Fuse is ECM 1.
C is the signal from the ESC to the ECM. Check for an open on this wire. Wire is Black or Yellow/Black.
D is ground. Brown or Black/Red. Check for open to ground.
E is the knock sensor signal. Check for open on this wire between ESC and Knock sensor. Dark Blue.

//2000CAYukon

Okay,

I was about to troubleshoot the connecter to the ESC module only to find out that there is no ESC module on my truck. I bought the truck about 2-years ago and evidently someone removed it or never replaced it for whatever reason. There is a 4-pin connecter that's just hanging out around the throttle body with nothing to connect to. I guess this is why the knock sensor is not getting a signal....

I called a chevy dealer and inquired about a ESC module and I was told that they did not put them on the 1995 and up but my repair manual shows one being there. I am not sure the next step to take in troubleshooting this.

My online repair manual indicates there were some with ESC and some with out in 95. ESC can also be known as Knock Sensor Module, just a quick education on terms. According to the schematic, there are 4 wires: 1. Pink, 2. Yellow with black stripe, 3. Brown, 4. Dark Blue. If these colors match the wiring on that connector you found, it most likely goes to the knock sensor module. The manual states the knock sensor module is located on the top right side of engine. The pink wire will have 12 volts coming from ENG-1; 20amp fuse (make sure you have power here). The brown wire is the ground (make sure it is a good ground connection). The dark blue goes to the knock sensor. The yellow with black stripe goes to the ECM (reports knock activity). Hope this helps.

Thanks for the response. I'll probably be this weekend before I can troubleshoot it.

My online repair manual indicates there were some with ESC and some with out in 95. ESC can also be known as Knock Sensor Module, just a quick education on terms. According to the schematic, there are 4 wires: 1. Pink, 2. Yellow with black stripe, 3. Brown, 4. Dark Blue. If these colors match the wiring on that connector you found, it most likely goes to the knock sensor module. The manual states the knock sensor module is located on the top right side of engine. The pink wire will have 12 volts coming from ENG-1; 20amp fuse (make sure you have power here). The brown wire is the ground (make sure it is a good ground connection). The dark blue goes to the knock sensor. The yellow with black stripe goes to the ECM (reports knock activity). Hope this helps.
On my '95 it is in the side of the block down by the starter. :wave:

Well i'm back again. I ordered an ESC module for my truck all the way to the exact part number and it's the same as the one from a local part shop which in turn doesn't fit the leads on my truck. My truck has 4 leads and the module has 5. I found out that all 95 models didn't have an ESC module so i'm assuming mine is one of those. Now i was reading my manual which leads me to believe i should check the map sensor and the ECM module. I have a voltmeter to check leads and what have you but my question is, How do i backprobe a wire? Is there some kind of special equipment i need besides the voltmeter?

I have know idea why my truck is still throwing a code 43. I tried everything I know to try. The map sensor and connector checked out just fine. I'm not sure if the ECM is damaged or not, all i know is that since i've changed the knock sensor I can't get the code to go away. Before, it would come on every blue moon so i just don't know. Thanks for everyone's help throughout this entire thread, i greatly appreciated it.

Is there someone out there that can me an idea of what the hell is going on with my trouble code 43. If you read this post, you'll see that there have been a lot of responses and they are well appreciated but i just don't know why this code won' go away. My truck is running great and i'm just confused. The only thing i hate is that i changed the knock sensor before checking the codes. As stated before in earlier responses, the service engine light was coming on periodically before i changed the knock sensor. Once i changed the sensor, it stays on constantly. I've traced the wire from the knock sensor and its fine. Could it be a defected knock sensor?????