Of Corvette's and Kenworths

"I've tried everything on this Corvette and I can't get the AC compressor to turn on. It had a bad programmer, so I put another one in. Then it had a bad pressure switch that caused the ECM to set a code 66. I cleared the code but the compressor still won't turn on. The HVAC programmer was $780 and I think it is defective, but I don't want to get another and find out that something else is the culprit."
Max is a good technician. He graduated with a technical degree in both auto and diesel technology and is willing to learn. Some of the older technicians, just like instructors, don't like change. Some--not all--are unwilling to get out of their comfort zones and in this business, that's a no-no. An instructor owes it to the students to keep current. Students are reflections of their instructors.
The HVAC programmer is a rebuilt part. It was an R-12 system I had a suspicion what it was. I pressed the fan up & fan down buttons simultaneously until-00 appeared on the HVAC display. I was now in diagnostic mode. Once in diagnostic mode, you can use the fan up & down buttons to scroll through the PID list. To view the value at the PID location, you press the AUTO fan button. I went to PID position 00: System Faults. I found )), which indicated no codes. Then I went to PID position 09: A/C System Mode. It was 01, which meant MAX A/C. The command was there. I moved to PID 11: Program Number, which represents a heating or cooling command. The programmer was commanding 00, a command for FULL COLD. I moved to PID 34: TEMP DOOR POSITION REQUESTED. It was at -155, which means when you see a minus sign at the value, you add 100. So, -155 was 255, which was FULL COLD.
Everything looked good. I remembered the hidden programmer code:48. When I taught HVAC controls in another lifetime, I called Code 48 the "Claude Rains" Code. the young technician didn't know who Claude Rains was.
"He played the invisible man in the movie back in 1933," I said. "It was a classic movie."
"Oh," the young technician said. It was way before his time.
I plugged the Tech 1 scan tool into the data link connector. First, I went to PID 00 and used the clear codes command on the HVAC head. Then I used the Tech 1 to clear ECM codes. Then I turned the ignition key off, took the Tech 1 off the data link connector, started the Corvette, and the compressor energized.
"How did you do that?" The wide-eyed technician asked.
"With experience," I said. "The code 48 was intentionally masked from the programmer's data list, but if it set, it sent a signal over the UART bus to the PCM to disable the compressor. Code 48 was identified as a LONG TERM FREON LOSS code."
"But I disconnected the battery. Wouldn't that have cleared the hidden code?" The technician asked.
"Sometimes, but not always," I said.
That was an easy one, but only because I learned the hard way on that one, all those years ago. We learn good lessons from our mistakes. We have to--so history doesn't repeat itself.
Onward to the Kenworth in my next post.
 

Tools of the Trade

Like every good technician, I have an electrical tool kit consisting of wire and terminal repair tools and soldering equipment. I also keep a stock of other materials, such as:

Stabilant 22:
This material is electrically active and stays resident within a contact pair, enhancing conductivity without leakage between nearby contacts. It's initially non-conductive, amorphous that becomes conductive when exposed to an electric field.

Rodent-Deterrent Tape:
This tape is treated with capsaicin to protect those wires with soy-based coating.

Liquid Metal Defogger Grid Repair:
Great for a variety of repairs.

Bare Conductive Electric Paint:
Like any other water-based paint except that it is conductive. I also have a conductive paint pen.

Nyogel 760G:
A silica-thickened, synthetic hydrocarbon grease to protect electrical contacts.

Silver Conductive Glue Paste:
Cures at room temperature and air dries.

Nickel-Copper Cobalt Tape:
Great RF shielding--70 dB @ 1 MHz and 100 dB at 1 GHz.

The 2016 Impala that I worked on had intermittently activated the SERVICE STABILITRAC warning on the dash and the sound of "electrical arcing" under the hood. My homemade, electronic electroscope detected
a spark from the inside hub to the outside ring on the harmonic balancer.

 

Measuring the resistance from the center of the hub to the outside ring of the harmonic balancer, I found about 763 K Ohms. I cleaned the harmonic balancer off with brake cleaner. Next, I used my liquid metal defogger grid material, applying it from the center hub to the outer ring on the balancer across the rubber to control the resistance. I told Samuel it is a temporary repair. The intermittent P0300 and STABILITRAK message was due to terminal fretting at the EBCM connector, terminals #23 and #24. My 40x illuminated loupe comes in handy for close inspection. A loose ECM ground caused the misfire at times--the P0300.

 

The problems with the Kenworth were resolved. The Service Lamp was flashing and there were transmission issues on the UltraShift transmission controlled by the TECU. The culprit was a corroded power supply to the TECU. The shop never suspected this because the wiring had been replaced before. But the root cause? I spotted the dirty powder on and near the wiring with my UV light (just another use for it). That was caused by nitric acid formed in the presence of moisture in the air. So, where did the nitric acid come from? It was caused by the ionization of nitrogen in the air, and that was caused by an intense electric field.

This diesel had some add-in inverters, causing nearby corona discharge, due to the close proximity of the wiring. Corona eventually causes punctures and carbon tracking. Whenever I see wiring in close proximity of other wiring, especially from an upfitter, I use my UV light to look for the residue.

A technician has to have good detective skills and be persistent. Had I replaced the power wire to the TECU, it would have failed because I would have treated the symptom, not the disease.

 

 

Electronic Heartbeat?

“It’s a 2016 International and it was parked out back for the weekend when a storm blew in,” Ketchum Jessup said as we stood by the truck. “I was havin’ me a cup of coffee, watching the storm, when a bolt of lightning zapped my truck. Struck the mirror on the driver’s side and blew the glass out,” he said, gnawing on a plug of tobacco. “After that, the truck wouldn’t even crank over.”

I looked at the documentation of other repairs. Every module on the J1939 data link had been replaced: the ABS ECU, Auxiliary Gauge Switch Pack ECU, the Body Controller, the ECM, the Electronic Gauge Cluster and the Pyrometer Ammeter Module. On the second visit to the shop, the Body controller, the terminating resistors and the J1708 data link had been replaced.

“It ran for a little while and then the Engine Stop warning turned on,” Ketchum said. “So I had a mobile repair truck come out.”

I saw that the Body Controller was replaced again, Ignition 1 relay and the Auxiliary Power relay. The BC supplies ground to the auxiliary power relay when the theft deterrent is active. Then the key is ON, the auxiliary relay is energized and the relay opens. When the relay opens it allows power to be fed to the Ignition Relay 1, the Crank Inhibit relay and the ECM. If the auxiliary power relay is energized, the vehicle won’t run.

“Now the gauges tick-tock as if they were on a clock or heartbeat or something when the key shuts off. Sometimes it starts, sometimes it doesn’t,” he said.

I checked for recalls, campaigns, safety-related reports and the like, but nothing came up during my research. I checked connections at the battery as a standard procedure. I checked all the fuses.

“Those are all basic checks,” Ketchum said.

“Exactly,” I responded. I used my inspection camera mad carefully checked all ECU connections, including the door pods. I visually inspected all ECU grounds. I was going over all worked performed by the other shops. You have to. The one thing that you fail to check will be the thing that gets you.

When I decided to check the terminating resistors, that’s when my ohmmeter readings were all over the place, as if I had current flow after everything powered down. I disconnected the battery and checked the terminating resistors. Individually, they measured 120Ω, which was good. But when I checked the J1939 backbone, my ohmmeter indicated OL.

 I reconnected the battery and started the truck. It ran fine for a few minutes and then the Engine Stop light appeared. I turned the key off and the gauges would jump periodically. I disconnected the battery and measured the resistance of the J1939 backbone again. Again it returned OL. Was the data bus open?

I manually ranged my digital meter to the 4KΩ scale. I measured the bus again and the resistance slowly climbed until it returned OL on the display. I reversed the meter leads at the diagnostic link connector, and the reading on the ohmmeter red a negative resistance, counting down to 0.00Ω. It reversed polarity and counted up again, until reaching OL. Now I knew what was happening.

My meter’s 9V battery was charging a capacitor somewhere on the circuit. When I reversed the lead connections, the capacitor discharged and then charged up again. Once the voltage reached the same value on each side of the dielectric, the capacitor was fully charged. The meter displayed OL. I decided to unplug each ECU, one at a time. I was also cross-checking each number. The fourth ECU I disconnected caused the odd reading stop.

Modern heavy-duty trucks can be described as rolling computer networks with seemingly endless possibilities for data collection and transmission. Many different devices found on trucks have the ability of collecting and storing this data when an event occurs. These devices are collectively referred to as Heavy Vehicle Event Data Recorders (HVEDRs). In most cases, however, an HVEDR is not a device but a software application added to an existing device that has an original purpose other than collecting and storing incident data.

Data collected and stored by HVEDRs can be useful when analyzing a truck crash. The most useful data comes from trip/event data recorders on engine Electronic Control Modules (ECMs) and wireless fleet management systems (a.k.a. tracking/ communication systems, mobile resource management systems, and telematics systems). These systems can record vehicle speed, brake usage, vehicle-use histograms, vehicle position history, active and historic diagnostic trouble codes, and more. An endless number of devices used on trucks that have a HVEDR function and no two devices record the same data. Therefore, an HVEDR is like a Christmas present where you really don't know what you're going to get until you open it. You may think you know what is in the box and sometimes you are right but often it is a surprise.

This truck went to a bodybuilder at some point. The ECU was added that acted as a dedicated HVEDR. It must have contained a capacitor that charged and discharged. I opened the ECU. I found a choke that was charging a capacitor due to a bad conductive trace so I removed the cap, repaired the trace, installed a new cap, and checked it again. The capacitor was now functioning as designed.

Ketchum held the cap in his hand. That little thing called all this grief?”

“To you and me both,” I said.

I'm pointing to the cap.