Erratic Electrical Truck - Don't Know What to Make of IT

[Ron Nielson]

Recently, my truck turned on the check engine light and there were some codes: P0108 Map Sensor High, P)128 ECT Low and P2563Turbo Pos SensorCircuit A High., all the involved sensors use the 5V Ref from the ECM. The truck ran just fine as far as I could tell. Never had codes like that in the past. I used my BlueDriver to look at the input for several 5V sensors that show live data in the tool. There isn't a complete match to the DTCs. What I saw was a rapidly varrying system voltage from about 12V to about 25V. I sent Blue Driver a message and asked them about this. Blue Driver was nice enough to look into my problem and sent me a new tool. Very nice of them. So I decided to do some data logging of some of the sensors to see what the values were.

ECT Engine Coolant Temperature, IAT Ambient Air Temperature, - those values should change over time as the engine and air temp rise but not fluctuate or go negative, but they did. They dropped down low and spiked.

BARO - should be very consistent, but drops and spikes there.
MAP and MAF - while these will vary with driving conditions, engine load, etc, again drops and spikes.

Control Module Voltage - Appears to be system voltage or battery voltage. This might go up and down depending on the conditions. Like the others, dropouts, and spikes. Battery voltage at almost 25V?? Where does that come from?

I went thru the datalog identifying and highlighting the erratic values of the various devices expecting to see a relationship between voltage and other aberrations but it only happened in a few instances. I spent a couple of hours preparing the spreadsheet and saved my work multiple times, but the program crashed, and my saves were not actually saved. Otherwise, I would attach the highlighted sheet with the problematic values for you to see. I did attach the raw sheet. It's a lot to look through but easy enough to spot the problem data points.

I note that MAP, BARO, ECT, and IAT are all 5V ref powered devices. I don't have a way to monitor these because it happens so quickly, way too fast for a DVM to capture and display. Now is when I wished I had a nice scope with graphing capabilities.

Any idea what could be happening to cause this? What to test to identify the problem(s) to be solved?

 

[2004LB7]

I suspect you have a sorting sensor or wire somewhere. I've heard of the oil pressure sensor shorting out and taking out several other sensors too since its on one of the 5v lines. You can always try disconnecting one sensor at a time and see of the problem goes away.

Also, I've heard of some accessory belts building up high voltage static charge and messing with some of the sensors and TCM. New belt fixed it.

 

[Ron Nielson]

I have been thru my engine compartment and recovered my electrical wiring with new split loom and Tesa tape. Did that a few years ago. That doesn't mean that there isn't a short somewhere. I use a Gates Green Belt serpentine because I noted at the time there were some belts that produced the static but the Gates did not.

I would think that if there was a short, it wouldn't be so temporary and/or set a code in that circuit.

When I started my truck today, I noticed a 'roughness' - almost a grinding sound and vibration --coming from the alternator that I had never noticed before. I replaced the original in August 2019 with a new ACDelco. Do you think this could be caused by the alternator? I still have the old one but it has problems.

My 'fear' is that it's the ECM. It's all 5V-related and very erratic. I'm not sure how I could replace the tune for my 'special' truck.

And THANKS for your thoughts.

 

[2004LB7]

If you disconnect those sensors with codes, do you still get the same or does it give you low voltage/performance/missing type codes? The ECT is different from the other too so maybe start there

I would assume it's a sensor or wire before the ECM. You can always try hooking up the ecm to a bench harness to see if you can communicate with it properly. Who did your tuning? Are they still around?

 

[Ron Nielson]

When those 3 codes appeared, I recorded them, did some preliminary checking, and could find nothing wrong. I deleted the codes. They have not returned. Battery voltages are good at rest, a little high when the engine is running - I'd like to see closer to 14.0 V. Almost no voltage drop from the Alternator to the battery. And I really don't understand 24+ volts anywhere.

AND THE TRUCK RUNS GREAT! And it probably will until we hook up the Arctic Fox and go on a big trip somewhere with no cell service and the wrong tools and supplies in the truck. Isn't that what always happens??

 

[Ron Nielson]

I'll try disconnecting those specific sensors and see what happens.

 

[2004LB7]

Weird for sure. I'm going to guess that 24v reading is an error. The batteries would clamp the voltage and keep it from getting that high even if the alternator was trying to push 25 volts. But what is causing it??? What about a bad ground from engine to frame or batteries? That would make the alternator output read low to the ECM and the ECM would try and increase output. May make the readings go up and down.

 

[Ron Nielson]

I don't recall when I last cleaned my ground for the EBCM, but the main battery to engine grounds have been cleaned several times and checked visually (effectively a gross corrosion check at best) many times. But they are on the list of things to do. I clean my at-the-battery grounds yearly.

I used to have a CTS2, but one day the connection cord from DLC to the CTS2 was smoking, literally smoking, I pulled the connector at the DLC to stop the heating and pulled the wiring to the CTS2 out from behind the knee bolster up to the dash. Thus, the DLC and connections are also on the list. When I use the BlueDriver, I get a 'filtered' view of the various electrical devices - everything goes thru the DLC circuit. The only way I know to get the true readings is to buy a scope and I think I'm just ordered a 2-channel scope so that I can see what is going on at each device or circuit. At about $127 delivered that would buy only an hour at a shop so it should be a good investment.Why this one? Ivan at Pine Hollow Diagnostics likes this one for an affordable easy-to-use scope. https://www.amazon.com/s?k=B0B497T6HR&crid=2Q0NGWQRMSDTD&sprefix=b0b497t6hr,aps,284&ref=nb_sb_noss

One thing I'd like to look at is a back probe of the power feeds at the ECM connector to the devices/circuits that Blue Driver says have a dropout or spike. If those devices actually have drops or spikes, I wonder where else I'm going to find them. And IF I find them, I'm not at all sure I'll know what is causing them. But it's like deer hunting - you have to find them first.

 

[1FastBrick]

With all of it being engine related, I wonder if there is corrosion at the fuse box junction point or one of the connections on the engine harness???

Do any of those circuits share a common point power or ground side?

 

[Steve9]

I have had a battery ground cable that "looked" fine-it was broke inside the insulation.

 

[Ron Nielson]

With all of it being engine related, I wonder if there is corrosion at the fuse box junction point or one of the connections on the engine harness???

Do any of those circuits share a common point power or ground side?

That was precisely one of my concerns also. Although I keep my engine pretty clean, the fuse block can be overrun with corrosion you don't see. So today I took it out and looked for corrosion, mouse nests, chewed wires, mud daubers, water, and anything that shouldn't be there. It was very clean. I sprayed the connectors with Deoxit and put it back together. Retested to see if any improvement - none to report. Still getting drops and spikes, and that even after removing power to all the easily accessible sensors and shutting off everything aftermarket, which isn't much in my truck: LED headlights, lift pump, Amp Steps. That's it. Going to look at the main grounds again tomorrow. And the cables themselves.

I'm beginning to wonder if all of our trucks have these drops and spikes and no one knows it?? You just wouldn't know unless you had a scan tool or scope with some graphing capabilities. I ordered a 2 channel scope today, just to give me some additional confirmation of what I'm seeing on the Blue Driver. And the scope allows me to test anywhere. I've owned this truck for 14 years and I've never checked, why would anyone else? My truck runs just great, it has been very reliable.

 

[2004LB7]

When you get your scope, let us know what you see

 

[Steve9]

You cannot tell if a cable is good by sight. Connections can be clean and tight, look fine but the cable deteriorates inside the insulation

 

[Ron Nielson]

The scope arrived today and after a little charging, I went to the truck. I was originally going to test at fuse 50 which is where the DLC gets its voltage readings. Then decided I should at last look at the source, the battery itself. I got a picture, but only marginally useful because there is no scale showing on the left side, the voltage is higher/lower. When testing with just the positive battery terminal unhooked, that horizontal line moved up and down a little. I expected it to be really flat; not so. Then I decided to detach the negative cable; better, but still not as flat as I expected. So I am still perplexed and need some help learning how to use and set up the scope. I wonder why the black wire attached to the probe with the alligator clip? I assume it grounds the probe? How or when would that be used? Well, the instructions that came with the scope don't tell me anything about it. I'll have to search for the answer.

I have a son-in-law here that is an EE. He specializes in power transportation, no 12V stuff, maybe 12KV stuff. but I'm sure he has used a scope in

school and may be able to help me figure out the answer.

 

[DAVe3283]

All meters/scopes need a ground reference. You'll want to attach that little alligator clip to ground (or a wire that then attaches to ground).

The scope probes usually share a common ground, so if you're using multiple probes only one will need the ground attached.

Without that you're measuring the voltage potential between the scope and the vehicle, which is going to float around randomly. Once you hook up a ground things will start to make sense.

Sent from my FlashScan V2 using Tapatalk

 

[Ron Nielson]

Thanks for that. Makes sense. Now to get the other settings correct.