TideLog Archive for August, 2014

Rikky recently bought a 2007 ADL Enviro400 that had the “Multiplex Communications Fault” and “Driveline Comm Fault” lights in the dashboard flashing. She bought it because “her cute nerd can fix it, right?” she asked me in her sweet voice, standing next to the recovery truck. I was flattered, but seeing as the bus wouldn’t even start, I wasn’t sure on the spot. Apparently one day it just gave up on the motorway, the old owners stuck it in the yard, forgot about it, then the company went bust. I simply sweetly smiled at Rikky, and said, “Yeah, sure, hun!”, as you generally do when a sweet girl you’ve known for years (and who is also my boss) asks you to fix something. Except I COULD probably fix it, being a massive computer geek. Vehicle embedded computer systems are as familiar to me as the ones you use in your office. Heck, she’d already paid £150,000 cash for it, which would buy my company shop twice over. Doesn’t sound so much until you think of the price of a house or shop! Unless you think of a modern double decker as a house on wheels, which is possible!

Rikky's Enviro400

The ignition comes on, all warning lights come on, some go out, as they’re supposed to. Turn the starter knob to “Start”, there’s no rumble, no life from the engine, just the communications fault lights flashing. The engine lights are still solid, as they don’t go out until the engine starts. No ECU fault codes either, and Alexander Dennis buses have a diagnostic switch in the electrical panel behind the driver’s seat that will flash a code via the engine management lights, so no laptop needed! Except there was no code stored, or it had been cleared. Damn. Over a few days of prodding and gently taking apart the interior to get to wiring, using my multimeter, I found what might have been the problem. The system wake signal cable from the engine computer was showing open when the starter was turned to Start. The signal comes from the starter switch, through the IOU (Input Ouput Unit) network, to the engine ECU, which then sends a signal back, to say “I’m awake, and initializing!”, where it then does a self test of its processor, RAM and ROM. If that test fails, the engine warning light flashes and the engine won’t start. Ours didn’t even get that far to do the test as it wasn’t being woken up!


Control units will go to sleep after a few minutes of non-use, they never fully turn off as they are always powered, like your desktop PC in sleep, they need a signal to wake them up. The brain for the engine was in a coma! This is why no fault codes were being set, and also why it wouldn’t start! I spliced and repaired the cable, hey presto, she started! BUT, a few days later, it broke down (on the darn motorway, just like it did for the old owners. The Police had to close the motorway for us to recover the damn thing!

The look that Rikky gave me at the scene saddened me, as though to say “You let me down, the Police had to hold people up because of you! You’re my nerd, why’s it not fixed?”. Aww, my heart dropped, I was ashamed. She didn’t have to say a word! It was fine in my roadtests though! She calls me Nerd affectionately, she’s the only one who says it sweetly! I don’t like anyone else calling me nerd, it doesn’t sound the same, when others do it it sounds patronizing.

This time, though, only the “Driveline Communications Fault” light was on, which took my instincts straight to the Engine ECU as that is the driveline controller! There was also fault code 111 stored, which according to my service manual, simply means “Internal hardware error, engine may die or hard starting” The “Possible no effect” bit was bollocks, a hardware error in the ECU will stop the engine dead as it will literally be brain dead as the injection is electronic as well as other sensors and stuff. Internal hardware error translates to “Self test failure” which is due, to hardware failure usually RAM!


About 5 hours later, under my (borrowed) oscilloscope’s sensitive nose, I found the REAL cause. The ECU’s oscillator was faulty and not ticking correctly. The crystal provides the computer’s heartbeat, so you can imagine what an irregular or non existant heartbeat does to an electronic device like a computer that NEEDS a heartbeat. They base the clock timings of other components on this main tick. 99% of electronic devices have a clock crystal. Humans couldn’t do without a heartbeat, neither can they 🙂 Engine ECU’s often have a second crystal, which the Cummins ISBe4 Euro 4 engine does, to generate clock timings for the injection. I replaced both, just to be safe!


I replaced the crystal, the bus is now running perfectly and has been for the last three days, and I’ve thrashed the engine driving it round the yard to heat the engine and computer up, it was likely because of heat it failed, ECU’s get VERY hot, the whole reason they’re in a metal case 🙂 Rikky’s happy, now her £150,000 investment isn’t scrap metal, I know she always has faith in me, if I fail, I try again and succeed 🙂

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I recently had a TideLog reader, Steve, contact me about his Menvier TS800 control panel, saying the panel was fine, but the charge voltage was intermittent, even with a new battery. A few days afterwards he dropped it off to me, lo and behold, just like the Optima, a worn resistor, under the keypad. Here’s a picture of what it should look like, and where it is located:

Menvier-TS800-resistors-locationThe one I’ve highlighted in green, labelled R52, supplies the +ve 13.6v feed to the battery, via D14 to the bottom left of it, which also seems to supply the telephone module terminal block with +ve voltage too. R83, which is the green resistor highlighted in blue, supplies the AUX 12v for PIR’s and such, and 12.6v to the bell.

Check both resistors, and all diodes for continuity and correct resistance, use my band code chart, in the Optima article, by clicking HERE. R52 on Steve’s board wasn’t badly burnt, but the resistor ceramic coating, along with the colour bands, had come off, there was slight burn evidence at the solder joints, and the voltage was stable until the board was under load, once the resistor warms up it breaks down when loaded with a flat battery on the charge rail.

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