Alien Makes and Models

“This one is serious, RJ,” the owner of a 2014 Kenworth said. “The EGR was non-functional, no DEF injection, reduced engine torque along with the MIL and STOP ENGINE light. Where do you start?”

The truck was a 2014 Kenworth, W900 Cummins ISX 15 CM 2350 truck. This one had a fault code 175 SPN 3464 FMI 3. The code indicated that the signal coming out of the throttle actuator is high. Considering that the throttle actuator was replaced three times, I strongly suspected it wasn’t the fault. I checked the terminals at the actuator and the ECM with my 40x magnifier, 25mm.—great for spotting terminal fretting.

 

We started by verifying the concern, followed by a thorough visual inspection. Research revealed no bulletins, although the Kenworth had a work history. The ECM was replaced and programmed. The throttle actuator was replaced three times, and a terminating resistor was replaced. I decided to decode the CAN bus packets, although I strongly suspected where the problem was—at the terminator that was replaced. I wanted to see how the data packets looked.

“What are we looking at? T.D. asked.”

“It is a Stuff Error, T.D. There is an issue with the terminating resistor that they replaced.”

This bit stuffing scheme is used to guarantee enough edges in the bit stream to maintain synchronization within a frame. If a listening device detects 6 bits of the same value, then it must have been the case that synchronization was lost and what was received was NOT what was sent! This is precisely what can happen with improper termination. Some bits in the frame are transmitted and received correctly, but the entire frame (and the integrity of all the bits in that frame) is not maintained and received at the listening CAN interface. 

Whoever worked on it before disconnected a 120Ω resistor, removed the other one and added two 120Ω resistors in series at one end. I didn’t know why. We repaired that issue.

Someone replaced the throttle actuator three times for a reason. My oscilloscope revealed AC noise to the neighborhood of 700 mV and that is a huge neighborhood.  The ECM was sending a regulated voltage signal out—dirty with AC noise of about 650 mV AC P-P. It was time to check the power feeds going into the ECM. Bingo!  The ECM power feed had about 500 mV AC ripple (the battery acts as a dampener, smoothing out AC current so a bad battery can cause strange symptoms in a vehicle). I had that condition on an Impala once. I checked the alternator with my scope: 1.2 volts AC!

Finally, the ECM ground had excessive voltage drop. After all the repairs, the Kenworth ran great. T.D. was happy to get it back on the road.

“Sorry you didn’t see any green aliens when you were here,” T.D. laughed.

“Did you ever see a UFO, T.D.?”

“No, but others around here have. There has been reports of saucers, cigar-shaped UFO, triangle-shaped, diamond-shaped and round ones,” He said. “We have a fair share of them.”

“You know what has always bothered me about the different shapes? I’ve always wondered if aliens have a choice of buying different models,” I said.

“What do you mean, RJ?”

“Well, we can buy an SUV, or a compact, or a sports car—and we can buy a Ford, Chrysler or GM; or imports. Judging by all the different UFOs, I just assumed that the aliens have choices of what to fly to our planet, T.D.”

He just shook his head.

Of Terminators and Characteristic Impedance

“Terrible what’s going on in this country,” Dan said, watching as I worked, tracing the data bus wires. “We’re proud of our heritage and now folks are taking it away from us,” he said as I worked. His truck had a DTC 148309, kept going into regeneration and he had it in to three different shops that replaced the complete aftertreatment system, including the doser valve three times.

“What do you think about all this stuff going on, Bob?”

“Actually, Dan, your truck is currently consuming whatever brain power I have at the moment,” I said.

He nodded. “I asked the technician working on it the last time to explain the J1939 data bus, but he wasn’t very clear.”

“The J1939 multiplexed chassis uses twisted-pair wiring, twisted to prevent the data backbone from acting as a radio antenna. The wires twist a through a full cycle once per centimeter on the backbone—2-1/2 times per inch,” I said.

My hand was getting cut up from the tight places I was going into.

“Those terminating resistors—they’re for signal noise, right?” Dan asked. “And the technician said they need to be 120 ohms, right?”

I checked V-CAN, E-CAN, D-CAN and A-CAN terminating resistance. The resistors each came in at 120-ohms.

“The truck J1939 data bus has a characteristic impedance of 120-ohms, but don’t confuse this with terminating resistors used at the end of the data backbone, Dan.”

“What is characteristic impedance, Bob?”

“It is just a factor of how a conductor appears to a high-frequency signal, regardless of length. You can’t measure it with a meter.”

Andrea, Dan’s wife, brought us some homemade lemonade. I loved her deep-southern accent. “Y’all thirsty?”

I thanked her and she noticed my bloody hand. “Y’all get into a cat fight?”

“No, just Dan’s truck,” I said.

Andrea offered to take care of the scrapes but I refused, saying that I was planning on getting a few more. She shook her head and went back towards the house.

“The terminating resistors also provide a low-resistive pathway for current flow between CAN H and CAN L. The capacitance can discharge and cancel rapidly,” I explained. “Of course, the length of time for a capacitor to drain is proportional to the resistance of the conductor it is discharging through. If capacitance can’t rapidly discharge when a component is trying to transmit at a low level, then the voltage differential between CAN H and CAN L stays high and that can shut down the data bus.”

“The truck has been stalling at times,” Dan said. “I had to disconnect the battery a couple of times to get it started.”

I scraped my hand up again, getting at the hidden wires while Dan held the light. “How do they come up with this impedance?” He asked.

“They do it by maintaining the dielectric constant, or wire insulation, and keeping the actual physical space between the two conductive wires constant by having a consistent twist pattern. Twist pattern is very important,” I said.

Then I found it. “Here is the problem.” I said. Someone repaired the CAN bus.”

“I could have told you that,” Dan said, “The dealer technician did it. He found some rubbed-through wire.”

“Yeah, but substituting ordinary wire for J1939 cables is a no-no because the dielectric properties of the insulation should be constant. You can corrupt communications on the bus by altering the impedance.”

“Corrupt? How, Bob?”

“Because the amount of time needed for every signal pulse pumped down the bus to neutralize increases; now the reflected signals scramble the data bus,” I said. I repaired the wiring, fired up the rig, and checked the data bus and all was well.

“I think we have it licked, Dan,” I said. Everything looked good.

We had great conversation later on over lemonade on the porch while Andrea insisted of doctoring up my hand. We talked about the protests and expressed feelings, but the world is tainted enough without letting it spill into my blog or Facebook.

Dan and Andrea are great people. I wish the world had more like them.  

Bearings and thrust washers destroyed by electricity?

A great friend of mine, Phil, reminded me of those golden years of the HydraMatic 350 transmission, used from about 1969 through 1984. It was typically paired with small block V6 and V8 engines. Although it was destined to become one of the greatest automatic transmissions ever built, we were having issues with the 350’s burning up back in the day.

I recall the first one I ever disassembled. Almost every thrust washer and Torrington bearing were wiped out. The old-timers out there, like my friend Phil, know exactly where I’m going with this. On the 350’s, it was due to a bad ground. Those pesky electrons were traveling through the shift cable, which was also failing, and transmission parts through the driveshaft and the rear axle.

The repair was installing two braided ground cables--one from the cowl (firewall) to the wing nut at the carburetor and the other was from the bottom of the cowl to a bolt on the bell housing securing the transmission to the engine.

As I explained to John and Greg here in Shepherdstown, some thrust bearing premature failures have been attributed by poor engine grounding. When the starter motor is engaged, electrons need to go to ground and if the engine isn’t properly grounded, current can run through the crankshaft and directly into the thrust bearing’s steel backing. In time, the thrust bearing faces can rapidly eat away, behaving as if the thrust surface on the crankshaft isn’t finished properly.

It’s simple and necessary to check for too much voltage in the drivetrain. You simply connect the negative lead of your DMM to the negative post of the battery, and the positive lead to the transmission. You should see no more than 100mv on your meter while the starter is cranking for about 5 seconds. Although the most current flow usually occurs while the starter is cranking, current in the drivetrain can happen while accessories are operating. That’s why you should perform this voltage drop test with the ignition on and as many accessories operating as possible. Again, the maximum is 100mv. If the voltage is too high, check or replace the negative battery cable, or add ground straps from the engine to the frame; or from the transmission to the frame. Some systems may reach 300mv briefly without causing a problem. For added assurance, improve the ground with a larger battery cable or additional ground straps.

“Is it possible that there is too much latent current flowing through the drivetrain, but without measurable voltage?” Greg asked.

“Sure,” I said, remembering one I dealt with about a year ago. “If you have a ground issue in the chassis, but the transmission and engine grounds are fine, the vehicle could pass the test, because the driveshaft and suspension components become the ground path. Saturn Vues going through wheel bearings can be the result of this.”

“So, how would you check that?” John asked.

“I pull the driveshaft and then measure the voltage drop. Now the frame and drive train must pass the 100mv test. Then you run a ground strap from the engine or transmission to the frame.”

“Remember the rear brake caliper slide pins freezing on W body cars years ago?” My friend Phil reminded me. “The engineers finally determined it was due to the static electricity created be the friction of the pads against the rotors looking for a ground through those mounting pins.”

John and Greg are great technicians who take pride in their work and I was glad to have an opportunity to help them out.

Haunted Car?

Can a car be haunted? On a muggy night in South Africa in 2004, a Renault Megane turned itself on and began jumping backwards, all on its own. This car is notable because there were several witnesses and news reports. Nine people, including two police officers, heard the Megane's engine start before it "jumped" backwards twice uphill, according to officials. The car apparently roared to life on its own, despite having no keys in the ignition and the parking brake engaged. I thought the 2006 Lincoln LS with a 3.9 was haunted. It came from Shepherdstown, a nearby town so haunted that the local police called in “Ghost Hunters” from the TV series. The LS Sport came from a couple of different shops for intermittent misfires, stalling, MIL on and transmission shifting issues. The work history indicated the plugs were replaced, TAC module was replaced, The PCM was replaced multiple times, the fuel pump replaced and coil assemblies were replaced. The throttle body was cleaned. Road test #1 resulted in an engine stall—just like the ignition was shut off. After the vehicle restarted, a P0607 flagged. The PCM’s internal CPU has encountered an error. This could be a calibration update, or aftermarket performance parts installed, or a damaged PCM. Clem came back with another PCM (number 3) and wants me to install it. I said no way. I did a visual inspection first, especially focusing on the PCM considering it was replaced before. Guess what? I found a damaged CAN (+) wire had several broken strands. I did a wire repair, confident that this was a major issue. I continued testing, though. I checked the ground circuits first. I prefer testing the ground circuits first because the remaining circuits will use this ground to verify they are working correctly.  This includes battery cable connections, which are subject to corrosion. No trouble found. Once the grounds are checked, I then move to the voltage circuits starting with B+ voltage because the Ignition, voltage reference, and control circuits require a functioning B+ circuit. B+ is direct battery voltage to a module or component. Those circuits were good. I checked the ignition circuits which includes ignition circuits that pass through a fuse, module, component, or connection.  When testing ignition circuits, I referenced the wiring schematic as to the ignition switch mode or position needed to achieve a valid reading. The ignition circuit test is referenced to the ground or low reference circuit and requires a functioning B+ circuit for a viable test. I checked the reference voltage circuit next, which is referenced to the ground or low reference circuit and requires a functioning ignition circuit. Satisfied that all PCM circuits were now acceptable, I moved on. Road test #2 flagged a P1270 (Engine RPM or Speed limit reached) and P2112 (TAC Control System). I checked data PIDs IACTRIM and IACKAM2. The sum of IACTRIM and IACKAM2 is the total IAC. Total IAC was 0.54 lb/min. I removed the throttle body and cleaned the edges of the throttle plate and throttle bore. It was bad. I reassembled it and took the vehicle on road test #3. This one resulted in an engine stall—just like the ignition was shut off. After the vehicle restarted, a P0607 flagged. The PCM’s internal CPU has encountered an error. This could be a calibration update, or aftermarket performance parts installed, or a damaged PCM. Clem wanted me to install that PCM. I said not yet. I already checked for the common bad coil issue. I always check the Coil-On-Plug ignition systems for defective coils by back-probing the main coil B+ with my PicoScope on glitch capture and using an injector as cylinder reference. I put the coils through the tests, including idle testing, cold, hot, snap throttle and power braking. With throttle cables gone, plus the 6-way BPPS, it is tougher to check these functions under the hood. I always look for a positive or negative voltage spikes on the coil ignition feeds which will indicate the failing coil(s). This car passed this test with absolutely NTF!

“This car is haunted,” Clem said.

“I have to walk away from it for a while,” I said.

“You can’t fix it?”

“No—I haven’t fixed it. I don’t throw in the towel but I do need a break.”

I thought about it while watching the Shenandoah River go by. A shop said they cleaned the throttle body and I could tell they didn’t. Did they even change the plugs? That was on my list of things to do when I would tackle it again.

“You must have one heck of a load, Bob, with all those cars and trucks to diagnose,” Clem said.

Then it hit me. I smacked my head as a token gesture.

“One heck of a load—you are so right, Clem!”

“Huh?” Clem said.

I got out my extra long test leads and went for a test drive. And I caught it--an ignition voltage spike! Right after the spike I lost the injectors. I also wanted to check that TAC module issue. With my PicoScope hooked up to ignition primary, and both throttle position signals (one on glitch capture), I captured a voltage spike on the TPS signal. The voltage spike is what caused the TAC codes.

The coil failed under a heavy load, hitting the PCM with the spike, causing it to reset.

More history of the LS Sport surfaced. The fuel pump was replaced because the original owner jump-started the car with a heavy-duty diesel truck charger on boost. Why did he do that? Because he was tired of the old battery going dead, procrastinating on buying a new battery, and after the original battery would take a charge, he decided to boost it. After that, he noticed the PCM would not drive the fuel pump so he had the car towed to a shop and had the technician replace the fuel pump.

The COP units were replaced, but a new one was bad to begin with, failing only under very high load. The ghosts were finally “exorcised” from the Lincoln.

I was so happy to get this one diagnosed.

“How can I thank you?” Clem was elated and hugged me and kissed me on the cheek. Now, don’t think that was weird. Clem is short for Clementine.

“You can really thank me by paying my bill, Clem,” I said, handing it to her.

“Now—that’s scarier than any ghost,” she said, after seeing it.

“I can put the ghosts back in the Lincoln, then.”

Clem paid.