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Master Tech Lee
Master Tech Lee, ASE Master Tech
Category: Car
Satisfied Customers: 582
Experience:  36 years Domestic and Import Electronics Diagnostic Tech
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Cadillac Deville: My cruise control doesnt work

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Once I'm at cruising speed, I press the "Cruise Set" button. The message "CRUISE ENGAGED" appears in the information center, but the speed will not hold.

I am checking on the codes. I will be back Leon


Codes are P0 code is an oxygen sensor code and the ao code is blend door circuit problem

I am looking into the no cruise with light on -Leon
Customer: replied 4 years ago.
Ok great. Thanks Leon. Let me know if you need any other information from me. I am somewhat car savvy, so I should be able to answer some basic questions if you have any for me about the car. - Shawn

Need you to check the basic things first. Lets check the vacuum lines first.

Customer: replied 4 years ago.
I'll check the lines as soon as I get a chance and let you know what I find out. It will likely be tomorrow evening before I get a chance. Other than the visual check, how else can I check the vacuum without an actual vaccum tester?
start engine and pull the lines to see if there is suction with your finger.

See you in the evening.

Customer: replied 4 years ago.



I checked the vacuum lines under the hood and they were good. However, both were unplugged from the servo! I hooked them back up and snugged the other connections (they were a not quite on all the way). Now the cruise works just fine. I drove it around town for about 30 minutes just to make sure. It slows down about 2 - 3 MPH from where I set it, but it's consistent. I would expect this to be somewhat normal on this age of vehicle. Would you say the same?


I'd like to ask a second question about the A040 code (blend door circuit problem). I can either close this one and open a new question or I can just raise the answer price to $56. Let me know what you'd prefer.


Thanks for the diagrams, they were extremely helpful.



Assume!! Glade i could help.

About the Ao code. I will be back in the morning to set up testing to remedy that problem. And the O2 code you might just clear the codes and replace o2 sensor.

You can raise the answer price. No sense starting over and we might loose each other to another expert.

Thank you so much, Leon
Customer: replied 4 years ago.

You are very welcome. I'm also glad you could help!


Good deal. If you could send me a diagram of where the left o2 sensor is, I would appreciate it.


About the Ao code: At first it seemed like my heater wasn't working at all. I changed the thermostat, and made sure the hoses going to the firewall were hot. Then I realized the passenger side heat works (but not at it's best). This is weird in itself because my year model has single climate control as opposed to dual. I took off the glove box and watched the actuator arm move back and forth. It seems like it struggles going from hot to cold but goes smoothly from cold to hot. Again, strange since the A/C blows nice and cold. I made a video of the actuator arm action. I can upload it here if you'd like, or I can post it on YouTube and send you the link.



ok i will - Leon Goodnight, Leon
Customer: replied 4 years ago.

When I raised the price, I didn't see $58 as an option, So I priced at $48 and will just give you a $10 tip to give you what I promised. Smile


No need to rush by the way. I'll be traveling immediately after work, but will be back in "fix-it mode" on Saturday.


Thanks again,



ok will do, Leon

Have a nice trip

I have to leave for two weeks my mom is not well need to go tend to her. If you still want me to help please rate me to stay connected. If not i will loose you to another expert. Sorry if i have caused an inconvenienced to you.



Master Tech Lee and other Car Specialists are ready to help you
Customer: replied 4 years ago.
No worries. I hope your Mom gets to feeling better. I'll be here when you return. Do you have any intuitive guesses about why the heater blows slightly warm on the passenger side, but cold on the driver's side? This is even with the heat all the way up. The higher the blower speed the cooler both sides get. My car does not have dual climate control.

Because of the bend door is not working correctly. Code AO40. I am still here until Monday due to the snow roads are bad. So When you are ready to start today let me know.

Thank you for the money $31.50 and bonus $7.50
Customer: replied 4 years ago.
You're welcome. I am ready. Do you want me to send you the video I took of the actuator arm action?
yes please
Customer: replied 4 years ago.

I ran it from hot to cold and vis-versa. It looks like it struggles going from hot to cold, which seems odd to me.
ok now at what temp setting ? arm is adjusting to the desired temp setting. If setting is set to the highest it should close the door to not allow any fresh cold air.
Need you to remove the arm from the blend door - move the blend door arm and tell me if it moves freely? if you feel some resistance then there is an obstruction - such as something fell into the defroster from top of dash into the blend house. If the arm moves back and fourth freely from one point to the other, then we have an ACP problem.
Customer: replied 4 years ago.

The door moves freely. What is ACP?

Air Conditioning Programmer - Do you know how to work the diagnostics from the climate control?
Customer: replied 4 years ago.

Oh, that sounds fun.


I have some basic instructions for it.

Do you know how to work the diagnostics from the climate control? yes lots of fun
Customer: replied 4 years ago.

Yes. I have some basic instructions for it:

ok i am sending this test to you please follow the steps accordingly, Leon

Attachment: 2012-12-30_205338_acp_test.pdf

Customer: replied 4 years ago.

Ok, I followed the steps. Here are the results:

Within 0 - 20 in AS12, AD23 matches accordingly. Between 21 and 78 in AS12, it struggles to match the commanded value in AD23 and will not settle within 60 seconds. From 79 to 99 in AS12, the value in AD23 remains at 78. Is replacing the ACP what I need to do now?

Yes AD23 remains constant at 78 you will need to replace ACPACP Location
Customer: replied 4 years ago.

I'm having trouble finding this part. Could you give me part numbers for a few different manufacturers?

I can not find it online either call GM Monday and also Call Rock Auto - I use Rock Auto most of the time to save on money and still get quality parts--[email protected]
1-866-ROCKAUTO (762-5288) (NNN) NNN-NNNNbr/>
I am going in the norning to moms - another storm is brewing so please when i get back that if you have not found one - i know i can.

HHappy New Year ! to you and family,

Customer: replied 4 years ago.

I think I found it. Is this it?

That is it great job, Leon
Customer: replied 4 years ago.

Cool. Can you send me some instructions for removing it please? I've been trying to figure it out and can't really tell what all needs to come off.


Also, could you send the diagram for the o2 sensor? Thanks and Happy New Year to you and your family as well. Thanks - Shawn.

Talk to you in two weeks, Leongraphic
Customer: replied 4 years ago.
Ok great. Thank you so much Leon. Take care. Hope your mom gets to feeling better.
Happy New Year.
You Bet!! Leon
Customer: replied 4 years ago.
Leon, I replaced the ACP as instructed, but when I ran the diagnostics test, it failed with the same criteria. The readout on ad23 still maxes out at 78 even though the blend door seems to move all the way over. How can I be sure it is all the way over?
hello i am back mom is better.

To check for full open - remove rod from blend door and move door to full open and mark the spot. Reconnect rod and run system and see if rod comes close to the spot you marked.
If it Does not come close please disconnect battery for 15 mins, then reconnect. Re-learn computer, start engine - drive 8 to 10 miles. At idle switch through all controls, heater A/C - temp selector from cold to hot vise versa. This will help computer learn its systems again.

I need to know is the cabin temp stable - is it too cold too hot?

Customer: replied 4 years ago.
Glad to hear your Mom is better. Moms are blessings. The cabin temperature is too cold. The passenger side is not quite as cold as the drivers side. I will check on the door position when I get home. How do I re-learn the computer?

Disconnect battery for 15 mins, then reconnect. Re-learn computer, start engine - drive 8 to 10 miles. At idle switch through all controls, heater A/C - temp selector from cold to hot vise versa. Run each selection for 2 min. This will help computer learn its systems again


Thank you,


Customer: replied 4 years ago.

Ok, sorry, I thought "re-learn computer" was a part of the process rather than the result of it. Thanks - Shawn

no problem
Customer: replied 4 years ago.


I verified the door is fully opening and fully closing all the way. Even with the temperature set at 90, cold air is blowing out of the drivers side. The passenger side is less cold, but not warm by any means. I'm going to go ahead and re-learn the computer anyway, just to see if it will help. What should I do if re-learning the computer does not help?

check the heater hoses from the engine area. the ones that go through the firewall, are they hot or is one hotter then the other? Trying to find out if heater core is working ok.
Let me know
Customer: replied 4 years ago.

The hose on the bottom side is very hot. The one on the top side is cool.

This sounds like a heater core problem. Cold one side the other hot - hot water flow is not circulating through heater core. Try flushing coolant first and if this does not work replace heater core. This vehicle does not use a Heater Control valve (Coolant Valve) as coolant is always circulated through the heater core. Rate of coolant flow through the heater core is established by the Coolant Flow Restricter. Temperature is controlled with the Air Mix Door which allows or restricts the flow of air through the heater core case.

Customer: replied 4 years ago.
How do I flush the coolant if I opt to do it myself?
I would run a five minute flush chemical like prestone from auto zone. read the instructions on bottle. The flush may help or not. Depending on the amount of debris clogging the heater core.Why the heat is felt some on passenger side is that the core is on that side, compared to the heat felt on drivers side. Most likely you will have to replace the core, esp if it is the original core. Did the code come \back in for the ACP?

Customer: replied 4 years ago.

Leon - I haven't seen the code come back for the ACP. I've been checking it every few days. I went ahead and bought a new heater core and will flush the whole cooling system since I doubt the car has ever been flushed. Would you recommend I do that before or after I replace the core? Could you send me instructions for replacing the heater core as well? Thanks, Shawn.

Here is the step by step fro removing heater core. Glad to know no code for ACP. I do recommend flushing the cooling system then replace core. If you need more help Shawn just ask. Leon



Remove the glove compartment and insulating panel.
Disconnect the rod to the blend door.
Disconnect the vacuum and electrics from the programmer that is to the right of the heater core housing.
Remove the 2 heater core cover screws and pull the cover off.
Remove the heater core mounting screws and lower the assembly out of the housing. Watch and protect carpeting from coolant leaks.


Heater Core R&R

Customer: replied 4 years ago.
How long should it take to change out the heater core?
about 1-1/2 to 2 hours

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