Write-Up: Series I Code 1640 - Finding a Fault

Ok I had the car scanned because it was showing SES light. Code 1640 cam up. Symptoms were SES light comes on after half a mile. Gear changes were all made ok with no stutering 40 down to 30.

Searching the internet gave me the following:-

PCM driver cct number 1 fail.

The relevant parts associated with this circuit are:-

TCC solenoid.
Canister purge.
Boost solenoid.

The Boost solenoid

The purge solenoid


the PCM viewed from the floor! with the "E" plug removed and is normaly hidden behind a panel (2 x 7mm screws holding it in place)


The "E" plug with tooth picks adjacent and marking required pins to test

Pin E9 - purge solenoid (dark green - white cable)
Pin E10 - Boost solenoide (grey cable)
Pin E12 - TCC solenoide (Tan and black cable)



All the solenoids are fed 12 V hot all the time and then go to the PCM to be switched to ground to turn them on.

Now the good book says to measure the terminals with respect to ground.
So volt meter set to measure 12V attach the black meter lead to ground and the red lead to eack of the pins above in turn with the ignition turned on you should measure the battery voltage (12 v approx).

This test can be misleading as i found out pins 9 and 12 were at 12.2 volts for me with pin 10 at 10.8 volts... close to 12 but no cigar!

A better test is to measure the current in the circuits.

Connect the black lead again to ground and set the meter to measure Current "I"
NB. my meter is capable of measuring 10 amps and was set to that range.

All the same pins should read greater than .4 amps pins 9 and 12 were .48 and .45 while pin 10 was 0 (zero) this means there is an open circuit on the boost line. the voltage measurement was because it actually was a hig resistance 5meg ohms which is for all intent and purposes an open cct!

so the boost solenoid was removed and measured for resistance and was found to be 4.5 to 5 Meg ohms. (new part on order from rock auto)

ACDELCO 214474 (214-474) Turbocharger $ 52.89

Strange name! but the same part. in the photo above i have removed the bracket that holds it in place, the replacement looks to be slightly different so may have to replace.

The TCC solenoid is in the transmition so would have been a so and so to remove... beware.

Any questions ????

Nigel

Thanks, Nigel! I'll add this in with the other write-ups. Nice pics of the PCM, btw.

great stuff friend.

Great writeup Nigel. I'm having this same problem now and your article was very helpful and informative. I do have one question tho. After you install the new BCS do you have to calibrate or adjust it in any way? Or do you simply install it, clear the codes, and drive away happy? Seeing the SES light on drives me crazy and I appreciate any help you can give in making it go away. Thanks

Derek wrote:

Great writeup Nigel. I'm having this same problem now and your article was very helpful and informative. I do have one question tho. After you install the new BCS do you have to calibrate or adjust it in any way? Or do you simply install it, clear the codes, and drive away happy? Seeing the SES light on drives me crazy and I appreciate any help you can give in making it go away. Thanks

i Just plugged it in cleared codes and away we go. i dont think there is an initalisation, if there is ive not done one.

I seemed to have gained an extra 1 - 2 MPG since doing the solenoide fitment was 14 at worst but has been 16 - 17 MPG now around town with 27 - 28 on longer runs best was 30 MPG.

Nigel

I've noticed a decrease in gas mileage as well. I was getting 18-19 mpg but since the code popped up I've been getting around 15. I'm hoping to get this fixed over the weekend. It was very helpful of you to print the part #, thanks. I'll post my results but in the mean time keep your fingers crossed for me.

Woohoo! Sucess! Ok so it took me a month but I finally got the SES light to go away. I got very lucky when it came to getting the part. As you all know the boost control solenoid is discontinued but I called my local buick dealer and he did some checking and told me that his system showed 1 dealership in the whole country that had exactly 1 on their shelf. Of course they were in California. Now even tho this part has probably been sitting there for years I immediately call them up in a panic, worried that someone else will snatch it up before I can. I spoke to the guy in the parts dept and he told me they indeed had the part and he would ship it out today and it would get to me in 5 days. Whew! But not so fast! Three days later I check and I was never charged for the part, so I call back and find out that the idiot never processed my order. Bad Freemont Chevy! Bad! Luckily nobody else swiped it out from under me. So the order is re-placed and I finally get my part. I couldn't believe how easy it was to replace. My mind was conjuring up all types of nightmares of what could go wrong, but in truth it took as long to disconect the battery as it did to replace the part. The whole process involves removing one 10mm nut, two vac lines and one electrical connector. Viola no more SES light! The car seems to be running smoother now with a noticable increase in mid-range power and throttle response. I'm curious to see if my gas mileage will go up as well. Thanks again to Nigel for his very helpful very informative writeup.

Thank you so much for this.

I take it you had the same problem. If you don't mind me asking where did you get the new BCS? Did you find a factory part or use the replacement that Nigel found?

Yeah, same problem.

I went to my local GM/Buick parts counter (McMaster Chevrolet in London, Ontario) and gave them the AC Delco part number referenced above. They ordered it for me and I had it two days later. Had to take the bracket off the old BCS and put it on the new one as the bracket on the replacement part is completely back asswards. It's pretty easy to take apart.. Just get out the pliers and pull up four metal tabs and it comes apart.

Sorry for my late reply, but I hope this helps.

Hello folks.
im getting the po640 code also. i pulled the BCS and put a ohm meter on it,and i came up with 9.8 ohms. i dont do the elec stuff very well,but i understand thats ok.im also getting a po131 low sig. oxy sensor. i guess im not too worried about that one,and a po171.
i am concerned with the po640,and im thinking it might be inj. related.i pulled one inj. at a time with the engine running, they all sounded pretty much the same.not one really stood out. any one out there have a similar problem with the 640 code? all help is appreciated and a 50%discount on any hooker for all correct answers when in vegas.dumb looks are still free

Robo, I've posted the schematic and the flow chart for this code (P1640 QDM No. 1 circuit) somewhere in the forum before. I'll post it again for ya.

Schematic


Flow chart

thanks A. i hate to sound like a dumb butt. can someone point out the location of the " evap purge valve" damned if i cant find it. does the 95 even have one? thanks a bunch

robotennis61 wrote:

thanks A. i hate to sound like a dumb butt. can someone point out the location of the " evap purge valve" damned if i cant find it. does the 95 even have one? thanks a bunch

On the back of the engine, on top of the right valve cover.
Follow the plastic line off the TB that disappears behind the engine.

sorry. i found it. i was having a moment,focusing on other things. im still running around trying to find the rough idle problem.she idles very rough,stumbling and threating to shut off. things quiet down when i put her in park. so..im thinking my CPS could be on its way out,or the BCS is taking a crap. after taking the BCS off the car and ohm testing it,its good. maybe its an intermittent failure of the BCS? any thoughts?

nigelf wrote:

Ok I had the car scanned because it was showing SES light. Code 1640 cam up. Symptoms were SES light comes on after half a mile. Gear changes were all made ok with no stutering 40 down to 30.

Searching the internet gave me the following:-

PCM driver cct number 1 fail.

The relevant parts associated with this circuit are:-

TCC solenoid.
Canister purge.
Boost solenoid.

The Boost solenoid

The purge solenoid


the PCM viewed from the floor! with the "E" plug removed and is normaly hidden behind a panel (2 x 7mm screws holding it in place)


The "E" plug with tooth picks adjacent and marking required pins to test

Pin E9 - purge solenoid (dark green - white cable)
Pin E10 - Boost solenoide (grey cable)
Pin E12 - TCC solenoide (Tan and black cable)



All the solenoids are fed 12 V hot all the time and then go to the PCM to be switched to ground to turn them on.

Now the good book says to measure the terminals with respect to ground.
So volt meter set to measure 12V attach the black meter lead to ground and the red lead to eack of the pins above in turn with the ignition turned on you should measure the battery voltage (12 v approx).

This test can be misleading as i found out pins 9 and 12 were at 12.2 volts for me with pin 10 at 10.8 volts... close to 12 but no cigar!

A better test is to measure the current in the circuits.

Connect the black lead again to ground and set the meter to measure Current "I"
NB. my meter is capable of measuring 10 amps and was set to that range.

All the same pins should read greater than .4 amps pins 9 and 12 were .48 and .45 while pin 10 was 0 (zero) this means there is an open circuit on the boost line. the voltage measurement was because it actually was a hig resistance 5meg ohms which is for all intent and purposes an open cct!

so the boost solenoid was removed and measured for resistance and was found to be 4.5 to 5 Meg ohms. (new part on order from rock auto)

ACDELCO 214474 (214-474) Turbocharger $ 52.89

Strange name! but the same part. in the photo above i have removed the bracket that holds it in place, the replacement looks to be slightly different so may have to replace.

The TCC solenoid is in the transmition so would have been a so and so to remove... beware.

Any questions ????

Nigel

I was wondering,if the BCS can be ohm tested off the car,why would one want to test it this way? couldnt you test the BCS,rule that out ,then move onto another problem?

A simple ohm test won't diagnose a BCS. You must use a vacuum gauge as well as a Meter. For shiggles, here is the BCS Flow chart (code P1257).

well..i did all the above and ive ruled out the BCS.

Okay so i scanned my 95 today and my code came up as p1640 QDM 1 failure. I am not exactly sure what this means. I also scanned KR and i could never get it to go above 0! i'm glad about that. I also scanned my girlfriends 95 and hers gave the code p0122 and said something about the TPS. Anyone have any experience with these two codes?

Was your SES light on?

A P1640qdm.Points to an issue within the computer,or its functions. My manual suggests,among other tests,that you hook up a Tech2 scanner and monitor the PCM. a mouthful for sure,I wish I could help but I dont have a tech 2 scanner.
some suggestions I came up with on a search--
What is the charging system voltage? Clear the codes, unplug the connector from the alternator and run the engine and see if the codes come back.

Another thing that you can try is called a tap test. Remove the ECM from its mount and leave it connected. Then start the engine and lightly smack the back of the ECM (opposite of the PROM cover) with an open palm. If the engine stalls out when you smack it, you might have a cracked board.

No need to replace the puter for this one. IIRC and don't quote me, but isn't 1640 QDM 1 the Evap purge, boost control and egr soleniods?

Each QDM controls 2-4 soleniods and when one is grumpy you get a code.

Watch those three items on the scan tool. Expect boost control to be at either 0 or 99 most of the time and EGR will only work under certain conditions, evap sol can be checked as well, I think the car has to be up to temp and running for at least a minute for the purge to work.

I have seen a Boost Control Sol act fine and cause this issue, but it could be any of the soleniods on that circuit. Do you have an FSM to double check which sols are on that QDM?

Thanks Robotennis, I am assuming that FSM means something like full service manual. I do not have one but i do need to find one. And yes my SES light was on and so was my girlfriend's. I am mostly sure that my ECM is not broken because i just had it replaced a few months ago. It was giving off a bunch of random codes and my dad's mechanic claimed the computer was shot. Any ideas on the p0122 code?

RidzRiv wrote:

Thanks Robotennis, I am assuming that FSM means something like full service manual. I do not have one but i do need to find one. And yes my SES light was on and so was my girlfriend's. I am mostly sure that my ECM is not broken because i just had it replaced a few months ago. It was giving off a bunch of random codes and my dad's mechanic claimed the computer was shot. Any ideas on the p0122 code?

fsm = factory service manual. In the meantime see if your local public library has a subscription to Chiltons on line or Alldata DIY, they have codes info and some troubleshooting. Although Chiltons "ChiltonLibrary" is a little weak - they don't show you how to replace the radiator for instance.

As for the SES light - when you are replacing components consider disconnecting the battery before working. Gets rid of the possibility of sending random transients thru the electronics and it lets the computer reset.

Thanks albertj, I will look into that.

So today i went to the junkyard that has a 95 riv, and i bought a throttle position sensor for my girlfriends car and an purge solenoid and a boost control solenoid. I changed the purge solenoid first, but the SES light came back on. Now i will try changing the boost control solenoid. I think this solenoid would make more sense because i seem to loose power during certain amounts of throttle.

Ok so today i tried to change my boost solenoid, but no matter how hard i pried i could not get the vacuum connection off of the solenoid. Does anyone know of a trick to get off stuck vacuum connections? maybe it is melted to the solenoid?

I finally got the solenoid changed and the SES light went out. The supercharger really does a lot now compared to before. It was like the supercharger was spinning fast but the engine wasn't getting the boost before.