TideLog Archive for the “Bus Service Info” Category

Rikku’s Volvo B7TL double decker has recently hit over 1 million miles, (yes 1 MILLION), and just today threw a Brake ECU message with yellow CHECK lamp. Her B7TL was the first double decker we bought in 2009 from West Midlands Travel, owned by National Express. Today I actually had time to do some pictures of the diagnostic menu.

It’s the most common “Check diagnostics for xxxxx ECU at next stop” message you’ll see, and as the brake system has wear level sensors, if you have drivers that don’t realise there’s a RETARDER (engine brake between the driveshaft and gearbox), they use the brakes too much and the lining wears out, triggering this fault message. It isn’t really a fault, but a friendly message to say, “Hey, your brakes are wearing thin!”

If you get this too much, you need to take your drivers into a meeting and tell them to use the brake pedal only half way for just the retarder! Pressing it all the way activates the service brakes as well, and can make the braking too bitey and uncomfortable for passengers. Retarders are great, they’re like using the gears to slow down in a manual car, saving the brakes.

The drivers always send me photos of the display at the roadside once they’re empty and pulled over safely, and I keep them as part of the service history, and they’re good for TideLog too, here you can see the message, plus the yellow CHECK lamp, so the vehicle systems are telling us gently there’s something needs replacing that isn’t critical, such as brake light LED clusters, or brake discs/pads:

The yellow CHECK lamp means a non-critical message or error. If the red STOP! exclamation lamp EVER illuminates, don’t do what First Manchester do and continue driving, you MUST STOP IMMEDIATELY.

So, I have trained Rikku and the drivers to be able to do basic diagnostics as they’re on the radio to us at Comms when out on the road. On the Volvos (B7TL, B9TL double deckers and B7RLE single decker) it’s really easy, you can do it using the steering column stalks without the IMPACT software on a laptop, that’s usually my job if I need to access freeze frame data from the systems when the error occurred, a bit like the flight data recorder of an aeroplane. Here the bus tells us what’s wrong, and as we’ve entered the diagnostic menu the yellow CHECK lamp goes out:

“Sensor lining left forward value too low. Active. Number of events 34”

This error basically translates to “Left front wheel brake wear sensor has detected brake lining worn past limit, error has occurred 34 times (ignition cycles) and it is still an active error.”

Replacing the brake pads and discs (I usually do all of them for safety in one go) recalibrating the sensors, and clearing the faults solves the issue!


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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 was on the 471 on Saturday on the way to Greg’s from Jenny’s, one of First’s Wright Urban Gemini bodied Volvo B9TL double deckers and as soon as I sat at the back, and the driver set off I knew straight away something was wrong. It juddered badly upon acceleration, and the engine was making a machine gun type noise whilst being sluggish. This told me straight away the engine had a problem, possibly a misfire.

The cylinders in Volvo engines can be shut off electronically by the Engine ECU if there’s a fault, so it could have been a result of this shut off caused by a misfire. The bus wasn’t in limp-home mode, it was still quite responsive. As soon as the driver let off the accelerator the shuddering stopped, so I knew it wasn’t a powertrain problem, so this excluded the gearbox, propshaft and differential.

It also couldn’t have been crankshaft or conrod big end bearing shells either. Anyway, being a respecting mechanic, as I got off I had this conversation with the driver:

Me: “I think you should call Comms and get this bus straight into the garage, your engine sounds like it has a misfire or internal problem.”

Driver: “A misfire, are you sure?”

Me: “Can you not feel how it judders when you accelerate, and stops juddering when you don’t? The engine sounds like a machine gun back there!”

I glanced down at his dashboard infodisplay, and sure enough the CHECK indicator was lit. There was no message displayed as he had it set to INFO rather than MESSAGES.

Me: “Even your CHECK light is lit. I’d call it in to be safe. If it gets any worse the bus computer will put the engine in limp home mode, you’ll notice it go really weak. The STOP exclamation indicator will come on your dash too.”

Driver: “Thanks for letting me know! How do you know all that?”

Me: “I work with buses like this nearly every day, for a friend in the Midlands”.

Driver: “Ah, it’s good to have guys like you to notify us of issues, us drivers can’t always tell there’s a problem when we’re in the cab at the front here. I’ll let someone know!”

Anyhow, I went on the 471 again yesterday to get to Manchester through Bury to get the tram to Manchester to catch a train to go back up to Birmingham, on the SAME BUS, with the SAME problem! It either hadn’t been called in, or it hadn’t been fixed! If that’d been Rikky’s bus, it would have been out of service within ten minutes of the problem being noticed, and wouldn’t be out again until fixed!

Just goes to show First don’t give a shit about a machine in their fleet that costs DOUBLE the cost of your average semi-detached HOUSE!! The single decker Volvo B7RLE’s are £130,000, and the doubles can be up to £200,000! It shows just how disposable they treat their equipment!

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I recently had to overhaul the steering system on Rikku’s B7R coach after it hit a very bad pothole, shattering the track rod & link rod balljoint cups. Here’s an article on my most common steering problems, causes and remedies. This article covers all Volvo coaches and buses with recent power steering systems, such as the B7R, B7RLE, B9TL, etc.

NOTE: If balljoints, joint cups or sealing rings are damaged the system should have parts replaced. NEVER repair damaged balljoint systems, as they will simply fracture again. Never re-use or repair gaskets, they are single use only. When inspecting, ideally you should steam clean or wash the steering system completely and use an infrared detector and magnifier to detect hairline cracks in the WHOLE system, including hubs and hub bearings as not all damage is obvious to the naked eye. Seizure of the hub shafts can result in a wheel coming off and a serious accident occuring, I have seen hubs sheared straight off due to fatigue at the hub shaft and the bus/coach has lost a wheel at speed when it finally gives way.

WARNING: This article is for EXPERIENCED mechanics familiar with bus steering systems and Volvo Impact software. You MUST ALWAYS follow Volvo’s guidelines for repair, bolt tightening torques, and always use GENUINE parts. Vehicle and passenger/driver safety can be compromised otherwise as the steering is a critical function of the bus that should have its safety and reliability maintained.

The steering and suspension of a bus comes under EXTREME stress under load at normal use due to bumps and uneven surfaces, NEVER overlook things that don’t feel right in terms of handling. This article only gives general guidelines, it is up to your judgement and professionalism as a mechanic to carry out the work.

Steering stiff in both directions

Cause Remedial actions
Oil level too low, or drops continuously when filled. Check and find any leakage in system and hoses/attaching bolts.Fill with oil and check the level of the reservoir. If the oil level continues dropping after being filled this is certainly a leak.
Air in hydraulic system. Check the reason and bleed the system.
Oil pump control valve sticks or oil drilling clogged. Disassemble and clean the valve and replace if necessary.
The filter is clogged. Ducts are obstructed. Change the oil filter and clean the ducts.
Universal joint hard to move. Check for interference.
Valve plunger stays open or leaks. Remove the plunger from the valve. Replace the plunger set.
The sealing ring at bottom of plunger not sealing. Replace. DO NOT attempt re-use or repair!
Plunger sealing ring damaged. Replace. DO NOT attempt re-use or repair!

Steering stiff in one direction

Cause Remedial action
Pressure limiting valves leaking. Replace the valves. For safety DON’T attempt repair, they are designed to be replaced.
Pressure limiting valves open too early. Check adjustment and adjust as necessary. Refer to Volvo Impact software for procedure.
Plunger sealing rings damaged. Replace. DO NOT attempt re-use or repair!
Cylinder lower chamber without pressure. Replace all sealing rings. DO NOT attempt re-use or repair!
Cylinder upper chamber without pressure. Replace all sealing rings. DO NOT attempt re-use or repair!

Steering heavy with rapid steering wheel turns

Cause Remedial action
Air in the hydraulic system. Check the reason and bleed the system.
Oil pump control valve sticks or has the oil drilling clogged. Disassemble, clean and make sure the valve works freely.
Servo pump oil flow low. Repair or replace the pump. Replace any sealing rings or gaskets. DO NOT attempt to repair rings or gaskets, they are single use only!

Stiff steering return

Cause Remedial action
Steering column shaft not lubricated or damaged. Lubricate, and if damaged with scratches or pits, replace the column shaft assembly.
Steering column not fixed properly. Check attachment and fixings, tightening as necessary.
Interference between spindles on fixing sleeve. Adjust.
Pressure point set too hard Check adjustment

Difficult to hold straight course

Cause Remedial action
Oil level too low. Check for leakage, top up the reservoir with oil.
Air in hydraulic system. Check for leakage and bleed the system.
Looseness in steering system Tighten the loose parts to correct torque settings given in Impact software.
Ball joint with excessive play. Replace. DO NOT REPAIR OR RE-USE DAMAGED BALLJOINTS, this is CRUCIAL for safety!!
Loosened connecting sleeve. Tighten the sleeve.

Impact felt in steering wheel

Cause Remedial action
Oil level too low. Check for leakage, top up the reservoir with oil.
Air in hydraulic system. Check for leakage and bleed the system.
Excessive play between worm shaft and piston. Check and adjust the worm shaft. If damaged with scratches, replace it.
Excessive play between sector shaft and piston Check and adjust pressure point.

Steering wheel vibration (Shimmy)

Cause Remedial action
Wheels unbalanced. Balance the wheels according to type of tyre and wheel manufacturer’s guidelines. This MUST be done correctly, as an unbalanced wheel puts stress on the wheel hub and shaft, possibly resulting in it shearing clean off with the wheel on prolonged use.
Steering out of alignment. Disassemble, clean and reassemble the steering using Impact software guidelines. Check it works freely and test extensively.

Steering wheel independently goes to either side (pulls)

Cause Remedial action
Oil level too low. Check for leakages, top up the reservoir with oil.
Air in hydraulic system Check the reason and bleed the system.

Oil leakage

Cause Remedial action
Reservoir cap loose Fix the cap or replace if worn/damaged.
Servo pump shaft sealing ring leaking. Replace the sealing ring. DO NOT attempt re-use or repair!
External leakage in power steering Replace sealing rings. DO NOT attempt re-use or repair!

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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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