A rear wheel speed sensor sends information to the ECM (correction). See C0055 00 - Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis

And see the attachment

 

A rear wheel speed sensor sends information to the transmission speed sensor. See C0055 00 - Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis

And see the attachment

The sensor reads 1440- 1460 ohms Also recently replace worn out rear brake pads. I sent enough fluid back to the master cylinder that some fluid over flowed the reservoir . I'm not sure that would matter. I drove the truck after that with no issues.

 

EBCM gets its rear wheel speed through the ecm. EBCM says it’s can’t communicate with the ecm. Locate and repair your loss of comm issue with the ecm and the C0055 will go away.

 

Where can I find a diagram for the ebcm connector?

 

I discovered one bad battery and the main wire to the alternator loose and looked burnt. So I changed out the battery and alternator. I noticed while the key was on the negative cable on the passenger battery was warm before I swapped out parts. It still was getting warm after as well. Service trailer brake came on also service battery system. Tomorrow I'll test for voltage at the ebcm.

 

Just below this:

 

Thanks Ron.

 

I'm going to get 2 new batteries. Its kind of a waste of time to do the tests with less the 12v.

 

So I picked up 2 new batteries. The only voltage I could get off pin 20 was battery volts. Test light didn't light. No volts with key on. Picked up a better scanner, but both codes will not clear. Truck has no crank or start.

 

Jeff - Which RPO braking system do you have? There are 3 different systems shown in the attachment.

Did you test the sensor itself? to make sure it was creating current? Remember that you need to set your DVOM to AC current to see what the wheel speed sensor is putting out. Once you are sure you have reasonable output from the wheel speed sensor, you can connect the circuit and do the other testing at the EBCM, based on your braking system. You will have to back-probe the desired pin to be tested. I would check all the powers and all the grounds, 5V references, and 12V references.

 

Jeff - Which RPO braking system do you have? There are 3 different systems shown in the attachment.

Did you test the sensor itself? to make sure it was creating current? Remember that you need to set your DVOM to AC current to see what the wheel speed sensor is putting out. Once you are sure you have reasonable output from the wheel speed sensor, you can connect the circuit and do the other testing at the EBCM, based on your braking system. You will have to back-probe the desired pin to be tested. I would check all the powers and all the grounds, 5V references, and 12V references.

I have JH7 JL1 I only did a ohm test on the sensor even bought a new one. I was testing with the ebcm connector disconnected. I'm not sure how to test the sensor on AC.

 

Jeff. Look at the video I posted. The wheel speed sensor actually makes electricity, and with a DVM you can see how much. Watch the video.

 

I watched it after I said I don't know how to test the sensor. It should be easy to do. I just have to raise the rear axle and put it in neutral. I sure don't understand the no crank , no start, but I'll figure it out it just takes me longer without the better scanners out there. The scanner I bought the other day scans all modules. I have some U codes on other modules. I'm not very fond of electrical issues. I appreciate all the advice you give me.

 

So I did the voltage tests on my pcm like in this video. I'm not sure it matters if its a gasser not a diesel, but I came up with the same results.

So I'm not sure I have a bad pcm or I still need to keep digging. I have started the truck with a push button remote on the starter, but the glow plug light stays on while running.

 

That's a very good video showing the basic steps with a test light and DVOM to check the circuits. No Scanner, no ociloscope. Straight forward.

Check pin 86 at the starter relay with the key turned to start and you should have power, circuit 625 yellow/black wire. If pin 85 is grounded, you should get power furnished to the starter, fuse 57, and that should feed directly to the starter circuit 6 a purple wire, and that hooks to the starter solenoid. It is somewhat common for the pin 85 line circuit 550 black wire to be broken or corroded and not furnish a good ground. You have already started the truck so if this part of the circuit is OK, you should have a running engine.

As far as the glow plug light, I don't THINK that's a problem at this point. You could pull fuse 6 and see what happens.

 

No power on pin 86 when trying to start. Pin 85 to 30 has power. I have power at the starter fuse as well. I tested 85 to engine with a ohm meter and it was good.

 

When you turn your key to START, the ignition switch passes power to circuit 1020 the pink wire to the BCM. BCM messages the ECM that you have turned the key to start. ECM has some checks like making sure the transmission is in neutral or park on circuit 1786 orange/black wire. If OK to start, it sends power to the starter relay on pin 86, circuit 625 yellow/black. You aren't getting anything on that pin so check to make sure it has a ground and that it is receiving power from the ECM. Something before the starter relay is not correct for starting. But you know if you manually power the relay, everything else works fine. Ignition switch? BCM? Transmission? They all have to work correctly.

Pin 85 to 30 has power.

Pin 85 is the battery cable supplying power to the starter when the relay is activated.

I have power at the starter fuse as well.

The starter fuse has power only when the relay is closed. You said you had no power on pin 85, I wonder what made the relay close and pass power to the starter fuse?

I tested 85 to engine with a ohm meter and it was good.

Pin 85 is the control (ground) side of the relay. It would have a circuit to the engine block or any other ground point - they're essentially the same thing.

I have no idea what tuner you have or its capabilities, sorry, just can't help there.

That chart is giving you the possibilities about what to check, to keep you from checking for impossible conditions. Unfortunately, U0100 shows up almost everywhere. In basic terms, if a wire has power and is grounded (shorted) you will have voltage up to the ground (short) point and nothing beyond. That is somewhat like a broken wire - power up to the break, nothing beyond, except that if you just insulate the grounded wire, the circuit becomes functional again, or repair the broken wire.

 

When you turn your key to START, the ignition switch passes power to circuit 1020 the pink wire to the BCM. BCM messages the ECM that you have turned the key to start. ECM has some checks like making sure the transmission is in neutral or park on circuit 1786 orange/black wire. If OK to start, it sends power to the starter relay on pin 86, circuit 625 yellow/black. You aren't getting anything on that pin so check to make sure it has a ground and that it is receiving power from the ECM. Something before the starter relay is not correct for starting. But you know if you manually power the relay, everything else works fine. Ignition switch? BCM? Transmission? They all have to work correctly.


Pin 85 is the battery cable supplying power to the starter when the relay is activated.

The starter fuse has power only when the relay is closed. You said you had no power on pin 85, I wonder what made the relay close and pass power to the starter fuse?

Pin 85 is the control (ground) side of the relay. It would have a circuit to the engine block or any other ground point - they're essentially the same thing.

I have no idea what tuner you have or its capabilities, sorry, just can't help there.

That chart is giving you the possibilities about what to check, to keep you from checking for impossible conditions. Unfortunately, U0100 shows up almost everywhere. In basic terms, if a wire has power and is grounded (shorted) you will have voltage up to the ground (short) point and nothing beyond. That is somewhat like a broken wire - power up to the break, nothing beyond, except that if you just insulate the grounded wire, the circuit becomes functional again, or repair the broken wire.

well I'm a idiot. I was testing the wrong fuse. I tested the abs fuse. The starter fuse has no voltage. Which as you said it should only have voltage when the relay closes. Now I did discover that the abs fuse has 12v both pins with fuse out. Which it shouldnt. So I turned the key on and check the abs fuse. 12v on one pin and 2.99v on the other. Turn the key off and back to 12v on both pins. I unplugged the ebcm and I only get 12v on one side of the fuse. So if the ebcm is shorted inside of the module would that cause no crank or start?

 

I connected it all back together and scanned all modules and I have these codes. u0100-71 , u0100-00 , B0158-05 , u3fff-ff That one I understand since my remote locks havent worked for a while. u0100. That one came up after I used a push button starter. Engine started right up. No fuel, oil pressure or temp gauges were working while it was running. Check engine light on brake and ABS as well.

 

U0100
Diagnostic Fault Information

Circuit​	Short to Ground​	Open/High Resistance​	Short to Voltage​	Signal Performance​
Module B+	U0100–U0299​	U0100–U0299​	—​	—​
Ignition	U0100–U0299​	U0100–U0299​	—​	—​
Module Ground	U0100–U0299​	U0100–U0299​	—​	—​
Accessory Wake Up Serial Data	U1814​	U0100–U0299​	—​	—​
High Speed GMLAN Serial Data Wake Up	U2099​	U0100–U0299​	—​	—​
High Speed GMLAN Serial Data (+)	2​	U0100–U0299​	2​	—​
High Speed GMLAN Serial Data (−)	2​	U0100–U0299​	2​	—​
Low Speed GMLAN Serial Data	1​	U0100–U0299​	1​	—​
1. Scan tool does not communicate with low speed GMLAN device 2. Scan tool does not communicate with high speed GMLAN device​

B0158 05 - Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis

 

U0100
Diagnostic Fault Information

Circuit​	Short to Ground​	Open/High Resistance​	Short to Voltage​	Signal Performance​
Module B+	U0100–U0299​	U0100–U0299​	—​	—​
Ignition	U0100–U0299​	U0100–U0299​	—​	—​
Module Ground	U0100–U0299​	U0100–U0299​	—​	—​
Accessory Wake Up Serial Data	U1814​	U0100–U0299​	—​	—​
High Speed GMLAN Serial Data Wake Up	U2099​	U0100–U0299​	—​	—​
High Speed GMLAN Serial Data (+)	2​	U0100–U0299​	2​	—​
High Speed GMLAN Serial Data (−)	2​	U0100–U0299​	2​	—​
Low Speed GMLAN Serial Data	1​	U0100–U0299​	1​	—​
1. Scan tool does not communicate with low speed GMLAN device 2. Scan tool does not communicate with high speed GMLAN device​

B0158 05 - Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis

Could I reflash the ecm with the tuner I have? Trying to find that short to ground is a bugger. Would alldata show me how?

 

I'm not sure about that. I THINK so, but that's really a guess. Maybe the wiring diagram will help plus the C0055 testing

 

I did the tests for C0055-04. I hope I did them right there kind of vague. #2 I tested 20 to B+ I get 12v. #3 20 to ground test didnt illuminate. #4 If all test are normal , replace pcm. It would be nice if it was just something simple like a ignition switch.

 

Do you have a way to tell if the mode switch in your trans is working correctly? If it shows in gear when you put it in park or neutral, that would produce the symptoms you have with no power to the starter relay and fuse

 

I can look tomorrow. Other then a my scanner no. I don’t get a code for it. That’s what my problem the last time I had no crank no start. It was a new switch. I put the old one back in and haven’t had a problem.

 

The mode light for what gear it’s in lights up. What’s weird is I don’t get any codes for the engine. I get codes for lost communication to the ecm. U0100-71 from the tccm and a u0100-00 from the tbcm. The tow truck did try to jump start the truck before he towed him home. I sure hope that didn’t cause all this mess.

 

The scanner should tell you somewhere about what gear is indicated by the TCM during the start sequence and another by what you see on the dash. When the 2 indicators don't match, the ECM will not start the truck. I saw this in a video recently. Just looked for it, but couldn't find it again.

 

That make sense. I better read the manual on the new scanner I bought. I'm not sure it will do that, but it does do more then most. I also need a wiring diagram for the rear speed sensor with 4wd

 

https://www.google.com/url?sa=t&rct..._ElectricalPickupsChassisCabs.pdf&usg=AOvVaw0N7QoZRarYgQo9OUzEK73B&opi=89978449

 

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiD_qLF7JWAAxV_nWoFHWZQCjMQFnoECBwQAQ&url=https://www.gmupfitter.com/wp-content/uploads/2021/05/2008_LD_ElectricalPickupsChassisCabs.pdf&usg=AOvVaw0N7QoZRarYgQo9OUzEK73B&opi=89978449

I have the upfitter book marked. The wiring diagrams are not easy to navigate. Today I decided to check voltage at the ignition switch. I have 5v at the white wire and 12v on the pink when the key is on. So now I need to track them to the ecm. For some reason the starter relay is not getting voltage to activate the starter.

 

Jeff

The ignition switch does not directly send power to the ECM. It sends power to the BCM and the BCM messages (GMLAN) to the ECM. See post #30 attachment. Also, see the attachments below.

I spent a couple of hours looking for the video I recently watched where there were 2 different indicators in the scanner that needed to match but were different, but I just couldn't come up with the correct video. I thought it was from South Main Auto, but maybe not. The problem they were trying to overcome is that they had no power to the start relay and all the power and ground checks came out OK. It sounded a lot like your problem.

 

Jeff

The ignition switch does not directly send power to the ECM. It sends power to the BCM and the BCM messages (GMLAN) to the ECM. See post #30 attachment. Also, see the attachments below.

I spent a couple of hours looking for the video I recently watched where there were 2 different indicators in the scanner that needed to match but were different, but I just couldn't come up with the correct video. I thought it was from South Main Auto, but maybe not. The problem they were trying to overcome is that they had no power to the start relay and all the power and ground checks came out OK. It sounded a lot like your problem.

Thank you I will check them out. I did notice how the GMLAN leaves the BCM to the ECM circuit 2500 tan/blk and 2501 tan. I planned on checking those wires today. I know I checked them at the BCM last time I had the problem.

 

This still going?

I have no idea what kind of scan tool you’re using but if you can pull codes out of the abs side, I’ll ask this simple question…..

Can your scan tool read data or codes out of any other module? More specifically, how about the ecm itself?

With both batteries disconnected, how much resistance do you have between terminals 6 and 14 of the data link connector?

 

Unfortunately yes. It’s still going on. I haven’t been working on it very steady. I hope to look at it some more today. I’m helping my pick pickles to can. The scan tool I have scans all the modules. I read 61ohms on 6 and 14. With batteries connected. I did get a code u0100 lost comm with ecm/pcm A and a tcbm u0100-00 lost comm with ecm I’ll check again later

 

So today. I checked for a signal from the ecm to the starter relay and of course I didnt get anything. Disconnected the batteries and put a ohm meter on the Gmlan and had 61ohms. I pulled my ecm just to see if it had a burnt circuit board. The cover did look like it was making contact with the board so I put some black tape there and reinstalled it. Then I scanned all modules. I get the same codes as before. Now when I just scan the ecm. I get communication error. So I turned the key off and on and get 8 codes plus on the dash it says reduced power plus service trailer brake system as before. Here's the codes p2227-00, p0047-00, p2565-00, p0118-00, p0090-00, p0851-00 and p0193-00 I think the truck is possessed. I didnt get any of these codes before I messed with the ecm. I dont get any codes using my old scanner other then the abs ones. Sorry for sounding like a kook.

 

Well I figured out what Frankenstein's problem was. The ECM connecter wasn't fully seated. My guess with the bumpy roads it wiggled loose to cause the ABS and the no comm's. I made sure when you push the bale closed on the connecters they were seated. Started right up codes were gone. Like it never had a issue. Now I just need to figure out the remote locks and the Hvac code. Which I didn't even know about. I think the remote locks have something to do with the cheapo ebay clock spring or the aftermarket radio. Seems like the key fob stop working around the time after the install of the clock spring and radio. Thanks for the help Ron and ChevyTech77