cruise control is out

my cruise control went out yesterday (which sucks b/c i drive 3k miles/month)and when i checked my SES light it says i threw a P0108 code which is all about the MAP sensor. the two are related, correct?

I already had a P0420 code which is related to the rear o2 sensor which i have been too lazy to replace. are the two codes related in any way? For the MAP code, i have not seen any degradation in mpg...but apparently i should be? i read somewhere, during my research, that when the MAP is out the mpg drops. mine hasnt but it's only been a day or so.

also, related to cruise control, i checked other things that people suggested like 3rd brake light, throttle cabling (the cable going to the module was a little looser than the cable going to the pedal - something to worry about?), and the brake fluid. they were all fine/normal

anything else i'm not thinking of?

car has 245K miles so i know stuff is going to start going out on me. ugh.

I would doubt very highly that the MAP and cruise control would be related at all. I understand the MAP is just before the cables and WAY before the BCM, but those are two diff systems.

iirc, the aft O2 is really not that crucial. it's only used as a comparison to the forward O2. as long as the fwd O2 is reporting good numbers, you should be good. for the degradation of MPG and power...I have no answer for you, sorry.

ummmm...why would the third brake light be a determining factor for cruise? good on ya for checkin them ANYway...but...huh? the loose cable I would address. for no other reason than because it MIGHT jump the groove and cause some bad juju to go down. brake fluid? who ARE these people?

all I can think of for cruise is cabling and the BCM. no, I don't know it all, and I'm not delusional to think that I even know a bunch, so I'm gonna let someone else chime in. but to try to connect the PCM and the BCM like that (MAP and O2 causing cruise issues), I think you're goin down the wrong path on this. good luck, please keep us posted.

i did some googling and that's what i came up with from some other grand prix forums. supposedly a safety measure built in with the 3rd brake light. and if fluid is low it was something about the pedal would sag and disengage CC like you were pressing the pedal. made sense in my head. there were some other ones like speed sensor that i didnt check.

i'll just have to suck it up and get it looked at this weekend. suck.

hold up on that. let someone else chime in. they'll be along in due course.

Did you check the fuse?

Your MAP Sensor sits above the PCV Valve; if the valve is sticking or plugged it could trigger a code: PCV Installation
I'd replace the valve, clear the code, and see if it comes back.

For the cruise control, if the brake lights are working, check the cruise control fuse with a test light, and try adjusting the cable:

Cruise Control Cable Adjustment (3800 L36 (VIN K), L67 (VIN 1))



1. Clamp the side of the cruise control cable adjuster lock with a pair of pliers and pull the adjuster lock out in order to disengage the cruise control cable adjuster lock (1).
2. The cruise control cable adjuster spring will remove the slack in the cruise control cable.

Remove as much cable slack as possible without moving the throttle lever.

3. Push the adjuster lock inward toward the throttle lever in order to engage the cable adjuster lock (2).

i did check the cruise control fuse and it was fine. i will try to adjust the cable after work.

when i took out the MAP sensor to look at it, the bottom part of the rubber/plastic stuff was torn a bit. it might have happened when i took it out but i dont think so. i might try just replacing the sensor.

AZ guys suggested i test for vacuum leak by spraying brake cleaner and i "think" my idle slowed down when i sprayed it but i'm not 100% convinced. i'm going to try it again with my dad and see what he says. idle should either speed up or slow down if there is a vacuum leak, correct?

thanks for the responses.

Idle will change if there is a leak. Usually it speeds up but if there is a noticable difference in rpms when you spray the suspected part then there is a leak.

how much of an idle change is significant and how long does the change last? couple hundred RPM's for a few seconds? my idle lowered audibly (i think) but then stayed there and didnt change again.

It usually increases for a very short duration. It uses the cleaner as a fuel so as long as your spraying it should increase. Once you stop it should slow down again almost instantly.

The only reason I can think the rpms would drop is if your "flooding" the cylinders. But that would be almost like dumping a jar into a carb to get it to do that.

@Blackarrow98GP: i tightened up the cable and nothing changed. thanks for the tip and pic, tho.

last night i replaced the PCV and MAP. this morning i cleared off the codes and drove it for a bit but nothing popped up. not even the o2 sensor code. drove around with a scanner getting real-time info.

MAP at idle ("Hg) 10.6-10.9
MAP at 3k rpms ("Hg) ~27
MAF (not MAP) at it's height was 9.x
the rest i cant remember b/c we couldnt save it

i drove the car for about 5 miles and restarted the car about 4 times during that time. the restarts during the test drive were hard starts meaning the car didnt start as quickly as it would normally and when it did start it would really thunk hard.

question: how long will it take for my car to throw a code if replacing the PCV and MAP didnt change anything?

It can take several trips, or drive cycles before the code(s) come back, if at all. If you want to speed up the relearn process, try this: General Motors Driving Cycle

I used this guide last year to get my car through emissions testing, after replacing the starter. After 4 highway trips of 18 miles each (1 per day), the car passed.

I'm not surprised that your car had hard starting problems; during my first highway trip I stopped for gas, and my car stalled as I pulled away from the gas pump. First time ever since buying the car back in '04..