DLC and serial data bus communication

Demigh55

Member
I have a 2004 Suburban 1500 LT with the 5.3L Vortex engine. Whenever I go through the automatic carwash, the kind that goes around the car and sprays high pressure water, my engine will start a random misfire and the check engine light will come on. The misfire will last only a few minutes or until whatever got wet gets dried out. I have a code reader but when I connect to the DLC it won't communicate with the ECU. My DLC has only 4 wires (no CAN) and when I test the pins with KOEO, no 16 has B+, no 4 has good chassis ground and no 5 has signal ground, but when I test no 2 it has less than 1 volt and fluctuates wildly. I realize that I should be getting 5 to 7v. I have tested around the coil packs by spraying a mist of water on each one with the engine running and wasn't able to detect a misfire, so I don't think one is cracked but I don't know what else it could be. Any ideas?
 
Last edited:

6716

Well-Known Member
Personally, I would avoid that car wash.:dance:

Can you pull the coil packs and inspect? I have the Atlas I-6, and I don't actually know if the coil packs on the 5.3 are similar or not. You might learn something there. How old are the coil packs? Might be worth investigating.

I had a Jetta that had a cracked coil with a corroded #1 chamber connection, that did a similar thing in heavy rain, misfired until it got dry. I couldn't see the issue until I started taking things apart.
 
OP
D

Demigh55

Member
Personally, I would avoid that car wash.:dance:

Can you pull the coil packs and inspect? I have the Atlas I-6, and I don't actually know if the coil packs on the 5.3 are similar or not. You might learn something there. How old are the coil packs? Might be worth investigating.

I had a Jetta that had a cracked coil with a corroded #1 chamber connection, that did a similar thing in heavy rain, misfired until it got dry. I couldn't see the issue until I started taking things apart.
I haven't pulled any of the coil packs as of yet but I think it might be a good idea. The truck has 185K miles on it and I replaced the spark plugs and wires recently. I'm more concerned about the other problem with the serial data communication with the various modules. The truck runs well but I seem to have a short to ground somewhere on on the circuit.
 

6716

Well-Known Member
Checking grounds is a solid plan with electrical issues. Wish I was more help on the serial data. @TJBaker57 has made some posts that make it seem like he knows some stuff about serial data.
 

TJBaker57

Well-Known Member
realize that I should be getting 5 to 7v.

You will not see those voltages unless you are using a scope maybe. The speed of the voltage changes between high and low state are just far too fast. In my testing I have seen maybe 3 volts amd only can see that by video recording the meter display for later review as well as initiating a lot of message traffic on the bus.
 

TJBaker57

Well-Known Member
I have a code reader but when I connect to the DLC it won't communicate with the ECU

So what code reader is it and do you have one of those inexpensive bluetooth elm327 clones? Can you test out the reader you have on another vehicle to see that it works?
 
OP
D

Demigh55

Member
The funny thing is I do have an ELM327 bluetooth adapter that I can use to get data with an app on my tablet, but the scan tool I have will power up and is unable to communicate with the PCM. When I connect it to my neighbors GM truck it connects and reads just fine however his truck has the advanced CAN protocol. My truck only has the J1850 VPW protocol and no CAN. All the research I have done tells me that when I test the pins in the DLC I should get 5 to 7 volts with KOEO between pin 2 and ground. BTW, thanks for your help!
 
Last edited:

TollKeeper

Gold Supporter
Since the ELM327 and the wired style OBD reader use both of the same operations, and pins, to scan the truck, I would see if you, or a buddy, has another scan tool. To me it sounds like the scan tool is the issue.
 
OP
D

Demigh55

Member
I have tried another wired code reader with the same result. Both are new and work on other vehicles but not mine. Both of them are Chinese made and it's funny that the bluetooth adapter can communicate but not the wired ones?
 
OP
D

Demigh55

Member
TJBaker57, thanks for your input and the video! I see what you mean about the voltage on pin 2, but I can't understand why my research insists that with KOEO, the reading should be 5 to 7v. I also wonder why my 04 Suburban doesn't have the CAN protocol when my neighbors 01 GM truck does? Anyway, at least my ELM347 bluetooth adapter will work with the app on my tablet. Thanks again for your help today.
 

Online statistics

Members online
3
Guests online
211
Total visitors
214

Members online

Forum statistics

Threads
21,447
Messages
612,193
Members
15,380
Latest member
Shaatt

Secure Browsing

Top Bottom