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4K views 25 replies 8 participants last post by  ewill3rd 
#1 ·
When driving the service engine light would flash for a half a second and then turn off. While it would flash the car seemed to have less power and the speedo gauge would drop to zero. Once the light goes out, the speedo goes back to normal but the trans will shift very hard. If I pull over and restart the car it shifts normally. It did the same thing yesterday while I was driving to Sacramento but the trans was not affected(as far as I could tell). I have a scan tool but its not showing any stored codes. What do you guys think? Is this a computer problem or is there something wrong with the transmission? Its a 2005 CTS automatic v6. The thing that sucks is I just bought it on Monday :crying2:


Edit: forgot to add, The problem comes up at random but so far only shows up while to car is moving.
 
#2 ·
Sounds like something with the ECU.

I had a similar probelm about a year ago but i was not fortunate enough to have my car start after turning it off. I was stuck in a gas station and decided to search the forums (via my cell phone) for this sort of thing. I ran into a thread that described a similar problem and it advised to simply remove the ECU fuse and put it back after a few minutes. I tried it and it actually worked. Never had the problem again.

Remember that if the car completely dies on you.
 
#3 ·
Thee manual states that the flashing engine light indicates a tranny issue. I had that happen to me when I red lined my caddi to get out of a semi's way. It came into my lane as I was coming onto the highway. I took it to the friendly neighborhood tranny shop. They test drove it and didn't find any issues after using tech2. You have to bring it in as it is happening I guess. but no issues from it since.
 
#4 ·
did the DIC say reduced engine power or anything like that?
ive heard of this happening before in other threads...not sure if the issue was properly resolved.
 
#7 ·
When the light comes on shouldn't there be saved codes? I thought I read here that some scanners may not pick up any stored codes. What scanners do you guys use? I bought mine a few years ago. Its a Innova 3100 OBD 2 scanner. Is there any way to retrieve codes without a scanner? Thanks for the replys.
 
#8 ·
When the light comes on shouldn't there be saved codes? I thought I read here that some scanners may not pick up any stored codes. What scanners do you guys use? I bought mine a few years ago. Its a Innova 3100 OBD 2 scanner. Is there any way to retrieve codes without a scanner? Thanks for the replys.
 
#9 ·
Sorry for the doube post above.

It did it agian while driving to work but this time it stalled while at a stop light. Service light came on and no DIC message. Once I restared(service engine light went off) the trans was hard shifting but did go away after I shut the car off and restarted.
 
#12 ·
I think he meant to say CKP which would be a crank sensor but that is a common issue on '03 only for CTS. The 3.6 doesn't really have issues like the 3.0 and 3.2 did.
There could be one of several things going on.

First of all the scan tool should be able to read not only ECM codes but TCM codes as well. CTS uses a module for engine and another for transmission.
The TCM may have codes... however if the TCM requests the MIL (check engine light) it should set a TCM requested MIL code.
One of a few things can be happening and the fact that an ignition cycle clears it is helpful but doesn't define the problem.
The trick would be to try to communicate using a scan tool while the car is acting up to see what is going on.
You could be losing voltage to a module, losing communication, or setting a code in another system that might cause the transmission to go to max line pressure.
The fact that the speedo falls off seems relevant too.

You need to get your hands on a scaner that will read TCM info or get the car looked at by a pro.
I'll certainly offer what advice I can but as stated, there could be a number of issues at play here.
 
#13 ·
What to do recommend as a good scanner? I'm looking for one I can run on my laptop or a stand alone scanner. There is one for the IPhone made by DevToaster that I may try out. I was planning on buying a good one anyways. The one I have now I bought in 2001 when I had my Saturn. Thanks.
 
#14 ·
I haven't used an aftermarket scanner for probably a decade.
Not sure that I could recommend any that would meet your needs. I have access to the factory scan tool that lets me check anything.
Maybe someone else has an idea but regardless of what you get, make sure it will read more than just ECM codes.
 
#15 ·
There are any number of cables for your laptop out there. Just search OBD II on google and you will find them.
Good think, unlike scanners, is almost all of them give you the software for free, which means free updates for life.
Bad thing, some of them might not work with all cars. I have one that reads my 05 CTS-V (and every other car I have tried) just fine. But it refuses to connect to my 06 CTS for reasons unknown. I gave up trying.
It really helped me though when I had my maxima, as I was having ignition problems, and I had it set up in the car as I was driving. It gave me realtime monitoring of engine speed, throttle position, spark advance etc.
 
#16 ·
The '05 V has a different PCM than the '06 CTS.
The '05 V uses Class 2 data and the '06 will be GMLAN or "CAN".
The '06 V got the newer computer and is now a GMLAN module.
That would be why your scanner doesn't work.

For '04 CTS and up you'll need a GMLAN, "CAN" ready scanner.
 
#17 ·
You just jogged my memory, so I went back to the website and looked. They have what's called an ISO cable, and a Tri-CAN cable. The ISO cable is half the price of the trican, so I had bought the ISO.

According to their website, if you choose 2008 model year, you have to buy the Tri-CAN. I imagine just about all cars now are using the CAN interface.
 
#18 ·
Yeah everything but the V and Escalade were using CAN from '04 up.
I think everything went in '06 but Escalade and then Escalade went for '07 with the new body style but I'd have to get the schematics out to be sure.
It depends on which computer they use and the V with the LS engine was a holdout.

I can bore you with all kinds of that crap but I think I'll stop here. ;)
 
#19 ·
Wow lot of info :worship:

I found a PC based scanner that says it does everything and will soon include ABS and airbags but its expensive. I may get that if I find nothing else. For now I think I am going to just drop it off at the dealer and get them to check for codes.
 
#21 ·
CAN is pretty awesome, it is waaaay faster than Class 2 and almost everything we have uses it.
Most of our vehicles have more than one bus of different types of data.

Most powertrain and fast acting systems like ABS are on the high speed CAN bus, some cars still have class 2 but only use it for generic diagnostic equpiment like Emissions testing machines or aftermarket scanners.
Entertainment systems and body communications are on a low speed CAN bus.

You can usually tell what your car has by looking at the DLC.
The pins in the DLC are all pretty much reserved and specified for configuration by ANSI. If a pin is in the hole you have it... such as...

Pin 1 is the low speed CAN bus, pin 2 is Class 2. Pins 4 and 5 are always ground and Pin 16 is always battery voltage.
Pins 6 and 14 are each half of the high speed CAN bus and there are some others but those are the main ones we deal with.

I love diagnosing communication problems but they are a lot easier these days than they used to be back in the old UART days with daisy chain data buses.... oh man that sucked.

On a side note the limit for a high speed LAN bus is 15. The new Hybrid Escalade has 30... they had to design a module to interface the two high speed buses together so it actually has two separate high speed buses but they are linked with a bus module in the middle somewhere. It is insane!
(not all 30 are on the high speed bus)
 
#23 ·
You can usually tell what your car has by looking at the DLC.
The pins in the DLC are all pretty much reserved and specified for configuration by ANSI. If a pin is in the hole you have it... such as...

Pin 1 is the low speed CAN bus, pin 2 is Class 2. Pins 4 and 5 are always ground and Pin 16 is always battery voltage.
Pins 6 and 14 are each half of the high speed CAN bus and there are some others but those are the main ones we deal with.
cool stuff; are you talking about the pins on the obd connector? I will have to look and see how many are present on my cable.

and I may have to upgrade my cable one of these days...
 
#24 ·
96 and up OBD II are all 16 pin.
I know those are all reserved for domestic and I think imports have to meet those requirements too.
Some pins are available for manufacturer use.
Not many...
 
#25 ·
So what is to stop a manufacturer from using their own proprietary connector? Do they have to have that connector present for federal emissions standards? I am guessing so, since IL plugs into that port for emissions test. But as long as they have that port for emissions info, is there anything stopping them from using a different port for other info?
 
#26 ·
OBD II regulations apply to anything sold in the US.
The 16 pin DLC is mandatory and as I said so are most of the pin assignments.
This is to standardize things. In the late 80's and through the 90's you had to have a myriad of different connectors to interface with different carlines.
Codes were crazy too, one manufacturer might use one set, while another would do something completely different.
Codes are also standardized.
U for communication, P for powertrain, C for Chassis, B for body and 4 digits which each have a meaning.
The first is a 1 or 0, 0 is a standardized code while 1 is manufacturer specific. The next digit is the system identifier and then a 2 digit code for the actual fault.
For non ANSI codes GM now uses "symptom codes" which are 2 digit Hex codes to identify specific faults, such as a short, an open, etc.
We are not allowed to use symptom codes for OBD-II regulated codes but we use them a lot for other systems to help isolate the root cause of a failure.

For a bit of info on OBD II codes check this link... http://www.obd-codes.com/faq/obd2-codes-explained.php
 
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