[1997_eldorado]

a bad module can also cause U1301 i believe
and if you can scan/view the individual modules it's easier to pin things down or eliminate them as an issue
spray that nut down with some penetrating oil and be careful not to go to hard looks pretty corroded....... maybe give it the once over with a wire brush

 

[geocoy2]

a bad module can also cause U1301 i believe
.
Well I believe I discovered what is going on. I tried to remove that bolt on the EBCM and it just refuses to budge. It is corroded right to the frame of the fixture it is mounted on. So I tried heating it gently and I used penetrating oil on it, I even tried tapping on it and I took a chisel to it. It is really stuck on its frame. So I sprayed penetrating oil on it and I went back to the ECM to see if I could take it off and clean it up better. Its mounted on a not very rigid frame that has four bolts pertruding thru the ECM. I managed to get the nuts off before but I wanted to see if I could remove the module and clean it up better. So the nuts come right off but the module will not budge off the frame. The bolts are rusted tight to the module itself. I managed to get one bolt loose so I could verify it should come right off, but the other three bolts are rusted tight. Im thinking if there is that much rust that is probably the reason they are not making good contact.
.
My strategy is to spray penetrating oil on the bolts and run the nuts on and off until I can break it loose, but right now I am not seeing any progress so far. If I accidentally break the module, the car is a tow away.
.

 

[Team ZR-1]

IMHO,
You're chasing yourself into the ground

The ECM gets ground from the ground splice pack and has several clean grounds going into it

You MUST stick in your debugging to what the DTC is, which you state is a U1301
Do nothing else but look at that

Check the class 2 serial data line for a short to voltage.
With your voltmeter set to min/max. KO / EO
What is the max voltage you get from pin 2 at the DLC connector.
Red lead to pin 2, black lead to ground.
That DTC says there is a high when it should not be

I explained in past posts you have to stick with the vehicles network,
If pin 2 is high, you might start by pulling one at a time a controller out of the network
Check pin 2 and also see if U1301 comes back or not
If the problem does not go away, then plug it back in and pull the next controller and repeat until
Pin 2 goes low.

Something is shorted to the network line and that would kill that controller from functions on
that Starbus but also screws up other controllers

I do not know where the Starbus network is for your vehicle, most cases it is next to the BCM as it is the commander/router of the network
Should be like several wires laying flat and has flat connectors for controllers to connect to

 

[geocoy2]

IMHO,

The ECM gets ground from the ground splice pack and has several clean grounds going into it

• 1) So your saying the ECM is using the post #73 in Plug C2 as its ground.
• 2) If that is true I can put the ECM back together

You MUST stick in your debugging to what the DTC is, which you state is a U1301

• Its my understanding that an error has to occur somewhere in the system to generate a U1301
• In this case a faulty groung could eventually create a U1301
• I understand your thought process that I should track down the cause/ or what generated the U1301
• Or in your words "Check the class 2 serial data line for a short to voltage."
• With your voltmeter set to min/max. KO / EO
• This is the Voltmeter I have there is no Min/Max KO/EO, so Im stuck

.

• What is the max voltage you get from pin 2 at the DLC connector.
  I have not opened the DLC plug
• 
  
• Red lead to pin 2, black lead to ground.
• That DTC says there is a high when it should not be
• If pin 2 is high, you might start by pulling one at a time a controller out of the network
• I have no idea what a controller is.
  But I understand your examination.
• Something is shorted to the network line and that would kill that controller from functions on
  that Starbus but also screws up other controllers
• Agreed,
• I do not know where the Starbus network is for your vehicle, most cases it is next to the BCM as it is the commander/router of the network
  Should be like several wires laying flat and has flat connectors for controllers to connect to
• I am working on the ground at the EBCM. the bolt is badly rusted and I need to get it loose and clean it up
• This bolt is listed as a Ground for the ECBM

One last point I wanted to make. I have the whole front end torn off the car so I can see most everything. I have found and cleaned all of the grounds in the Engine Bay except for the #8 on the pic below. It is the ABS ground. Thats what I have been working on the last few weeks. I just want to get it cleaned up so I can cross grounds in the engine bay off my list. It is my thinking that the root cause of this problem came from my recent work when I changed out the Catalytic converter. I was not having any issues before that. All of that work was in the Engine Bay.

 

[Team ZR-1]

Do NOT confuse the BCM, body controller to the
EBTCM that handles traction and ABS controller

If your multi meter does not store min/max then you simply have to write down what the min and max voltage you measure when trying to debug your class B problem

They call it a Starbus network, would be if you drew a line from one star to another, so they are in series
and then there is a return line to complete the data path, that would be the BCM

IF let's say star 2 (controller 2) or its wiring gets screwed up than it opens up that series path and all controllers suffer

The protocol the network using (older vehicles use GM's VPW and SAE's "CAN" each controller every few seconds puts out a SOH (State Of Health) frame, that is to let the other controllers know it is working fine.
If BCM does not see that from a controller it than that controller is no longer functional, when it really is, but the network is screwed up like in your case and simply that controller's SOH does not travel through the Starbus network

Without seeing how your controllers are wired for the network or what voltage is supplied, I cannot tell what would be the correct voltage to see on class 2, but I suspect 5 volts or fewer ?

You should tell when you do your testcases is one by one taking a controller out of the Starbus and what you measure on pin 2 of the DLC what voltage change you see

 

[geocoy2]

Do NOT confuse the BCM, body controller to the
EBTCM that handles traction and ABS controller
.
Sounds like you are saying a "Controller is a Module".
For instance the:

• The EBCM is a module.
• The ECM is a module

And if this is correct, my test procedure would be to unplug the EBCM and test to see if I have the correct voltage in teh system. Is this correct?

 

[Team ZR-1]

Yes, pull one module at a time and test pin 2 for less 7 volts
Class 2 functions from ground

I suggest you read closely the 2 attached PDFs on GM Class 2 and how it functions

 

[geocoy2]

Yes, pull one module at a time and test pin 2 for less 7 volts
Class 2 functions from ground
.

• Well, I put the ECM back together and I apparently shook something up. I decided to hook up the Code reader to see if anything changed.
  First thing I notice was the key comes out of the ignition without using a tool. Not sure what I can conclude from that since the ignition switch was operational before that, it just would not allow me to remove the key.
• So I hooked up the code reader and I have a bunch of new codes we were not seeing before.

• P2138	Accelerator pedal Position Sensors 1-2 Not plausible		Generic Stored
  P0641	5 V Reference 1 Circuit		Generic Stored
  P2108	Throtle Actuator Position Performance		Generic Stored
  U0100	Lost Communication with ECM		Generic Stored
  P0641	5V Reference 1Circuit		Generic Pending
  P2067	Fuel Level Sensor 2 Circuit Low Voltage		Current
  U1040	Lost Communication with EBCM		FSC DTC
  U0100-00	Lost Communication with ECM		Cadillac MIL
  MIL = Malfunction Indicater Lamp	Check Engine Light

 

[geocoy2]

New Edit

 

[geocoy2]

Do NOT confuse the BCM, body controller to the
EBTCM that handles traction and ABS controller

Without seeing how your controllers are wired for the network or what voltage is supplied, I cannot tell what would be the correct voltage to see on class 2, but I suspect 5 volts or fewer ?

You should tell when you do your testcases is one by one taking a controller out of the Starbus and what you measure on pin 2 of the DLC what voltage change you see

• Using this video, I tried to start the process of testing
  
• WITH KEY OFF
• There is 12 volts on pin 16
• Tested Pin 4 to 5 yes there is continuity
• Tested Pin 4 to 16 yes 12 Volts
• Tested Pin 6 to ground = no reading
• Tested Pin 14 to ground = no reading
• Tested Pin 5 to ground 5 millivolts
• Tested Pin 4 to 16 Yes 12 volts
• Tested Pin 5 to 16 Yes12 volts
• Tested Pin 4 to 5 = 3 millivolts
• WITH KEY ON
• Tested Pin 4 to 14 = 2.6 volts
• Tested Pin 6 to 14 = 150 millivolts ???

.

 

[Team ZR-1]

• Using this video, I tried to start the process of testing
  
• WITH KEY OFF
• There is 12 volts on pin 16
• Tested Pin 4 to 5 yes there is continuity
• Tested Pin 4 to 16 yes 12 Volts
• Tested Pin 6 to ground = no reading
• Tested Pin 14 to ground = no reading
• Tested Pin 5 to ground 5 millivolts
• Tested Pin 4 to 16 Yes 12 volts
• Tested Pin 5 to 16 Yes12 volts
• Tested Pin 4 to 5 = 3 millivolts
• WITH KEY ON
• Tested Pin 4 to 14 = 2.6 volts
• Tested Pin 6 to 14 = 150 millivolts ???

.

I have stated multi times the U code is saying CLASS 2, the video you point to is testing the CAN buss

I have stated multi times you need to look at pin 2, and it should NOT be staying at 7 volts, should be ramping up and down

You need to work with this video, and again I mentioned you need to get to the Starbus network and use the test connector there as you see in this video but first is seen what pin 2 is outputting

Watch this video multi times if need be to understand how to determine if a module is bad, constant chatting or wire shorted

 

[geocoy2]

I have stated multi times the U code is saying CLASS 2, the video you point to is testing the CAN buss

I have stated multi times you need to look at pin 2, and it should NOT be staying at 7 volts, should be ramping up and down

• In your video the man is Grounding one Probe and then he starts with the Positive probe at the first pin on the splice pack and he checks for a test reading that is modulating up and down. If the reading is not modulating up and down it likely has a problem. Then he moves to the next pin performing the same test. He seems to be saying you check all the pins.

.
In your commentary you say we should be using only Pin #2 The Buss Positive Pin. Can you explain?

 

[ELDORADO2K]

Wait, you just lost me…

 

[geocoy2]

I have stated multi times the U code is saying CLASS 2, the video you point to is testing the CAN buss

You need to work with this video, and again I mentioned you need to get to the Starbus network and use the test connector there as you see in this video but first is seen what pin 2 is outputting

• So I tested like the man shows in your video and these are my readings
• #16 pin = 12 Volts
• #15 pin Not used
• #14 pin = 2.64 Volts (Chassie Ground)
• #13 pin thru #7 are Not Used
• #6 pin = 2.8 Volts
• #5 pin = 135 Ohms
• #4 pin = 0
• #3 pin = Not used
• #2 pin = Seems to be modulating from 0.8 to 1.9 Probably hung on a Low
• #1 pin = Not Used

So it looks like we need to go back to #2 pin and start pulling Modules to see which Module is causing the problem

 

[Team ZR-1]

Yes, if the KO EO when you were testing and voltage is going up down but not going to 7 volts than
a short to ground you assume

You need to find the Starbus network and the test splice pack to take modules out of the network and then test each one of that pack to find who is causing this as you know if valid talking on buss the volts would be going to about the 7 volts

Not sure if this would work but instead of pulling the cap of test splice pack is
what if the fuses for modules one at a time, would the low voltage on pin one go away ?

Maybe not as if it's a wire shorted to ground, it still is even if the module's fuse is pulled ?
Might be a quick test to find that out but if you have easy access to the Starbus test pack
I would test there

 

[geocoy2]

Yes, if the KO EO when you were testing and voltage is going up down but not going to 7 volts than a short to ground you assume
NEW EDIT
You need to find the Starbus network and the test splice pack to take modules out of the network and then test each one of that pack to find who is causing this as you know if valid talking on buss the volts would be going to about the 7 volts

Might be a quick test to find that out but if you have easy access to the Starbus test pack
I would test there

• I don't know what a Starbus is, or what it looks like
• I assume a Starbus is a wire harness

NEW EDIT
So I Performed the test we talked about, Pulling the Controllers/ Splice Pack out of the modules and see if one of them causes a change in the low readings
.

• Just to be clear the original reading I got when I tested the DCL at pin #2 was .8 to 1.9 fluctuating, so we decide it was likely a wire to ground but at what module.
• The ECBM controller made no change when I pulled the Splice Pack Connector
• I pulled the Connectors for the Cam Sensor and Mass Air Flow connector, only because I had re-wired both of them. Just wanted to be sure they were not part of the problem.
• I pulled C1 Top connector on the ECM and it had no effect
• I pulled C2 the middle connector on the ECM and the reading changed drastically. The new Reading jumped to eight (8.54)
• I pulled C3 the bottom connector and it had no effect on the reading
• I pulled the connector for the transmission Control module and it had no effect on the reading.
• So I assume we can conclude there is likely a short to ground in some of the wiring to the C#2 connector. How do we determine what wiring is leading into the C#2 Connector?

Pin	Wire Color	Circuit No.	Function
1-2	--	--	Not Used
3	D-GN	485	TP Sensor 1 Signal
4	PU	486	TP Sensor 2 Signal
5-7	--	--	Not Used
8	L-GN	432	MAP Sensor Signal (I worked on this)
9	--	--	Not Used
10	YE	573	CKP Sensor 1 Signal
11	L-BU	1876	Knock Sensor 2 Signal
12	GY	23	Generator Field Duty Cycle Signal
13	GY	1716	Low Reference
14	L-GN	5282	CMP Actuator Solenoid Control Exhaust Bank 1
15-16	--	--	Not Used
17	TN	1744	Fuel Injector 1 Control ( I worked on the Fuel Injector Fittings)
18	OG/BK	1745	Fuel Injector 2 Control
19	D-BU	496	Knock Sensor 1 Signal
20	L-BU/BK	1746	Fuel Injector 3 Control
21	OG/BK	877	Fuel Injector 7 Control
22	L-GN/BK	845	Fuel Injector 5 Control
23	YE/BK	846	Fuel Injector 6 Control
24	D-BU/WH	878	Fuel Injector 8 Control
25	D-GN	5273	CMP Sensor Signal Exhaust Bank 1
26	--	--	Not Used
27	BN/WH	5303	Low Reference
28	GY	2303	Low Reference
29	PU	5284	CMP Actuator Solenoid Control Intake Bank 1
30	YE/BK	844	Fuel Injector 4 Control (??) not sure about this
31	OG/BK	5272	CMP Actuator Solenoid Control Intake Bank 2
32	OG	5275	CMP Sensor Signal Intake Bank 1
33	D-BU	5300	12-Volt Reference
34	WH/BK	5283	CMP Actuator Solenoid Control Exhaust Bank 2
35	TN	5301	Low Reference
36	OG/BK	469	Low Reference
37	TN	2752	Low Reference
38	TN	2761	Low Reference
39	BN/WH	2130	Low Reference
40	L-BU	5302	12-Volt Reference
41	PU	574	Low Reference
42	BN	2129	Low Reference
43	PU	5274	CMP Sensor Signal Exhaust Bank 2
44	TN	582	TAC Motor Control - 2
45	GY	5296	Low Reference
46	L-GN	5298	12-Volt Reference
47	BN	5299	Low Reference
48	YE	581	TAC Motor Control - 1
49	YE	5276	CMP Sensor Signal Intake Bank 2
50	L-GN	1867	12-Volt Reference
51	GY	2701	5-Volt Reference
52-53	--	--	Not Used
54	YE	410	ECT Sensor Signal
55	D-GN/WH	428	EVAP Canister Purge Solenoid Control
56-57	--	--	Not Used
58	PU	2121	IC 1 Control
59	OG/WH	2122	IC 2 Control
60	OG	2127	IC 7 Control
61	L-BU	2123	IC 3 Control
62	D-GN/WH	2124	IC 4 Control
63	PU/WH	2128	IC 8 Control
64	D-GN	2125	IC 5 Control
65	GY	2704	5-Volt Reference
66-67	--	--	Not Used
68	OG	225	Generator Turn On Signal
69	L-BU/WH	2126	IC 6 Control
70	--	--	Not Used
71	YE/BK	5297	12-Volt Reference
72	--	--	Not Used
73	BK/WH	1551	Ground

believe this is a 2004 connector 2

 

[Team ZR-1]

So in your testing, you believe the short on class 2 is from the ECM ?

All class 2 on the Starbus and the splice packs for the modules shown here
You need to save these and then enlarge to see them better as this forum limits photo sizes
Go back and review my posts as I showed what each wire is for the ECM,
Look at the splice packs below for Starbus/Class b
ALL Class B wires are purple

 

[Team ZR-1]

When you tested for the ECM where the other modules plugged back into the Starbus ?

When you read pin 2 of DLC at 8 volts, was the voltage from ECM steady or was the reading jumping up and down ?

Look at that video again when they talk about voltage staying high of a module

 

[geocoy2]

• When you tested for the ECM where the other modules plugged back into the Starbus ?
• 
  
• When you read pin 2 of DLC at 8 volts, was the voltage from ECM steady or was the reading jumping up and down ?
• 
  
• Look at that video again when they talk about voltage staying high of a module
• 
  
• By the way, the ignition was in the ON position.
• Yes, I plugged each module back in after I tested it and before I tested the next module!
• The voltage at 8 volts was steady.
• Will check out the high reading in the video.

 

[Team ZR-1]

So that would mean the ECM outputs about 8 volts constant, so it does not shut UP
the prevention the other modules cannot talk via class 2 on Starbus

As you recall from that video modules talk, then voltage goes to like 0, another module than can talk but if ECM is always high and hung up

Watch video from like 5 to 10 minutes into the run