TideLog Archive for the “Dennis” Category

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 love the Dennis Dart! It is such a quick bus, especially given that at 11.2m long it is only 800cm shorter than a normal city bus. It feels like you’re driving a car, the engine is so quick, and the body so light. Rikku bought her Dart two years ago, it’s a 1996 P reg, I completely overhauled the engine and gearbox, it failed an MOT for the previous operator and they decided to scrap it. It was sat there all sad and lonely in the scrapyard when we went to buy a ZF gearbox for one of our Volvo B7RLE’s, I couldn’t let it get crushed, neither could Rikky, she thought it was cute! It came home to the garage with us, I overhauled it completely, now she’s in regular service as a Bullring Centre shuttle bus!

I raced Rikku’s 1996 P reg Dart against her 2009 59 plate Volvo B7RLE last year, the Dart left the Volvo in the dust! The Volvo B7RLE has a Volvo D7E290 inline 6 cylinder, 318kw Euro 5 engine with ZF 6HP550 6 speed gearbox. The Dart is only a Euro 2 spec 6-cylinder 108kw Cummins with 4 speed Allison gearbox! It has less output power and less gears but still managed to outrace the Volvo! Even when they’re both up to full speed on a runway the Dart stays ahead of the Volvo!

That day was so much fun! Rikku lost a bet, she bet that she’d beat me by driving the Volvo, and I gained £10 as lunch money in the canteen!

The thing I like about the old Dennis Dart is there is none of the modern multiplex computer controlled stuff in it like all Rikku’s modern fleet, there’s just an engine ECU and a transmission ECU for the auto box. There’s none of the new common rail injection either! As much as I love multiplex systems, and common rail electronic injection, it’s nice to go back to the days when it was just you, the engine/gearbox, wheels and road, with no computers controlling the experience, telling the gearbox or engine how to react. Dennis sure know how to name their buses. Since the partnership of Alexander the bus body manufacturer, and Dennis, to make the Alexander Dennis company, the Dart is still around! Yep, the Enviro 200, 300 and 500 still bear big resemblances to the old Dart, in both interior and chassis. The engines are much more up to date, they have all multiplex systems, and the vehicles are a bit heavier, but the old Dart still lives on…

Anyway… One of Rikku’s contacts in the bus industry sent me the Dennis service manual a few days back, which is a godsend, because Rik still uses the Dart on our Bullring route, a lot of elderly people use it and they like the Dart because it is roomy and a very low floor. I’ve had to use pure guesswork servicing it as there are no manuals on the web. So, this is my first article! I’m not allowed to distribute the manual, Dennis will kick my butt! I don’t wanna upset them as I love their customer service and buses, so if you need help, ask and I’ll do an article!

My first article is on changing the drivebelt, as it is a consumable part!

Models Covered: Dennis Dart SLF SPD (Super Low Floor, Super Pointer Dart, with Plaxton Pointer body)

Chassis Models: SFD466BR1*GW3, SFD466BR1*GW4, SFD476BR1*GW4, SFD476BR1B*GW4, SFD476BR1B*GW3, SFD477BR1*GW3, SFD477BR1B*GW3


Visually inspect the belt. Pay close attention to the ridges on the underside of the belt that sit in the grooves of the pulleys.  Check the belt for intersecting cracks.  Transverse cracks (across the belt width) are acceptable.  Longitudinal cracks (direction of belt length) intersecting with transverse cracks are NOT acceptable.

Renew the belt if it is frayed or has pieces of material missing, or damage to the tensile members in the belt, these are crucial for friction. I always like to replace them as soon as they start squealing, but always check the tensioning as this sometimes causes belt slip, not wear. Letting the belt slip can damage it too because the belt gets hot and disintegrates.

1. Check that the master switch is at OFF with the engine stopped. Let the engine cool, as the belt and pulleys of all driven components will be very hot, especially if the belt has been slipping.
2. Using a bar from a socket set, in the square hole in the arm, turn the automatic belt adjuster clockwise to remove belt tension.
3. Holding the adjuster in the raised position, remove the old belt and fit the new one, ensuring that the belt seats correctly in the grooves in the pulleys. A misplaced belt will damage pulley bearings, and the tensile memebers in the belt itself.
4. Lower the adjuster on to the belt and see that the belt is adequately tensioned.

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