TideLog Archive for September, 2011
Posted by Tidosho in Bus Service Info, Volvo, tags: accelerator pedal, B7R, B7RLE, B9TL, buses, faulty, limp home, safe mode, Volvo
The accelerator pedal on Volvo buses is electronic, and I’ve seen cases where the potentiometer in the pedal has gone faulty. This results in the bus going into limp-home mode, which is like a safe mode so you can get the bus safely back to the depot for repair. But, many drivers wrongly assume that the turbo has gone faulty, as this can cause the bus to go into safe mode like most other engine faults including fuel supply and injection.
In this article I’ll explain exactly what makes the pedal work, and all systems involved.
The electronic accelerator system allows the driver to provide manual control of the engine speed, and thereby the speed of the vehicle.
- The Accelerator setting & fault indication is only present on Volvo buses equipped with automatic transmissions or I-shift.
- The IVS, CAN and J1708 connections differ between Volvo EMS1 and EMS2. EMS stands for Electronic Management System, known in the industry as Multiplex.
- The engine must be running.
- The transmission is in gear (D, or 1, 2, 3 ratio settings if available depending on the make of transmission fitted. Some ZF and Voith auto boxes have just P, R, N, D.
- Vehicle speed must be higher than > 5 km/h for the system to be fully active
The following control units are involved:
- Vehicle electronic control unit (VECU)
- Engine electronic control unit (EECU)
- Gearbox control unit (TECU)
- Brake control unit (EBS5)
- Body builder module (BBM). Also known as Body Control Module or Unit
The accelerator pedal is connected to the VECU via two hard-drawn signals, one digital (IVS) and one analogue. The analogue signal is generated by the pedal’s potentiometer and the digital by an engine idling switch. If a fault occurs in the potentiometer, the digital signal takes over so that the vehicle can be moved (known as Limp-home function). The digital (IVS) signal enters via a port in the VECU, which in turn is connected to the body contact block (BB1:1).
The analogue signal is converted in the VECU to a percentage value that is sent to the EECU via the control link. As a safety measure, the accelerator pedal position is also sent via the information link. The EECU uses the message to set the engine speed.
Buses equipped with automatic transmissions have a kick-down (downshift) function. When the accelerator pedal is fully depressed, the VECU software registers this as a kick-down and sends a message via the control link to the EECU and the TECU. The TECU ensures that the automatic transmission drops down a gear to give the driver higher engine speed and faster acceleration. Kickdown is also initiated when the bus is driven up a hill and acceleration is slow in mid/high rev range. This is normal, not a fault!
Accelerator pedal, fault indication
Volvo buses equipped with automatic transmission or I-shift have a function to switch out the requested throttle setting if both the accelerator pedal and the brake pedal or parking brake are activated at the same time.
The function is activated when the accelerator pedal is pressed at the same time as the brake pedal is depressed and the speed exceeds 5km/h. When the function is activated, the driver is informed via a warning on the instrument because the engine brake cannot engage while acceleration is taking place, the accelerator must be released first.
The function is deactivated when the accelerator pedal is in its idling (fully released) position or the ignition is switched off. If the fault comes up in the cluster even though the pedal is released, have the pedal looked at. The bus should always go into limp home if the potentiometer is defective. If it doesn’t there may be a fault in one or more subsystem ECU’s.
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Older scripts still use this, and it’s causing me headaches. Luckily I found out why it’s happening. Recent versions of MySQL require you to use ENGINE=MyISAM instead.
Simply load any.sql or .php scripts into a text editor, and use Find Replace! Replace all instances of TYPE=MyISAM with ENGINE=MyISAM and your problem will go away!
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This is to be carried out when squealing can be heard, either with the engine started and running, and/or on kickdown (downshift) on hills. Belt squeal signals that the belt needs replacing and/or re-tensioning. This only applies to the alternator belt, on the B7RLE the fan belt is toothed, and lasts much longer.
If the belt is left to deteriorate, loss of battery charge will result as the alternators struggle to turn, thus not keeping the batteries topped up, resulting in complete power loss, or failure to start the engine due to inadequate start capacity in the batteries (around 50% in a twin battery & alternator vehicle). Note I now grayscale all my service pictures, people were complaining they were taking too long to load!
1. Switch off the bus engine, and allow to cool. Alternators, engine and belts will be HOT.
2. Open the bonnet, and locate the fan belt. This needs to be removed first to get at the alternator belt as they overlap each other.
3. Loosen the fan belt tensioner, the location of which is shown above, and gently remove the fan belt. If it requires replacement, now would be a good time to get out the replacement belt ready for fitting!
4. De-tension the alternator belt tensioner and lock it with a M5 bolt (1). This prevents it going out of alignment.
5. Remove the belt from around the alternators, guide pulleys and cam pulley, after removing the fan belt the same way. My picture shows the fan belt still on, because I took the pic before removing it!
6. Clean all pulleys to remove dirt and rubber debris using a clean rag. DO NOT use LIQUID or GREASE/OIL anywhere near the belts or pulleys! They are designed to run with friction in the tension of the belt, getting liquid or grease contaminants anywhere near will cause the belts to slip and compromise the effect, and will mean a ruined new belt, the pulleys may also need to be replaced!
7. Re-assembly is the reverse of removal. Check the belts are tight, routed correctly and that all bolts are secure.
8. Start the engine of the bus using the underbonnet starter panel, let it idle for 3 minutes, then rev it erratically on and off with varying pressure on the accelerator to check for squeal. DO NOT go over the redline rev zone (above 3,500rpm), engine damage will result.
NOTE: Failing belts may not always be the cause of sudden or gradual power loss, or loss of battery charge. This could indicate either A). Faulty batteries, or B). Faulty alternators. I recently serviced Rikku’s 08 plate B7RLE after we suddenly lost all engine and electrical power on the motorway. One of the alternators had failed completely causing overcurrent, tripping the control relay, shutting the alternators off from the battery charge system, so use your judgement, and a voltmeter!
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The tailor has sent us a picture of what Kassie’s Supergirl outfit will be like once it is finished! He makes custom fancy dress costumes, but they are very expensive, as they are true to life, very accurate and precision made. Here’s what her outfit will look like, this is another he has made for a girl as petite as Kass:
She is going to look so sweet as Kassie-Zor-El! I’ve always wanted to see her as Supergirl, because to me she is my very own real life Supergirl, and this costume is perfect! She’s only tiny, 160cm tall (5ft 2″), so we had to have one custom made, all our other costumes are for much taller girls. The boots are being made last, and we have a waiting time of 3 months due to the tailor’s backlog, but it’s going to be well worth it.
This outfit is being made to withstand wrestling and getting messy, we told the tailor what our shoots on the new site are going to involve, but it still looks waaayy too cute to get dirty! I hope Shannon goes easy on Kass when she duels her in a gunge match for the first time! It’s the outfit I’m worried about, we all know Kassie can hold her own in wrestling, with her kick-ass Martial skills, so she might fight a little too eagerly!
I’ll just have to let my imagination run wild until the costume is done!
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Awww, I couldn’t resist when I saw lovely Christine Bleakley (pronounced Blakeley) in the paper the other day, in her cute school uniform!
She’s such a cheeky gorgeous chick, I’m even more in love, her smile melts my heart like a kitten does 🙂
She had a visit to her old school Bloomfield Collegiate in Ballyhackamore while filming a “back to school” segment for her breakfast programme Daybreak.
The cutest ever, isn’t she?!? Now all she needs is a real man in her life, rather than a money focused, treat-women-like-meat fairy footballer prick like Frank Lampard.
Chrissy babe, my number’s in your blazer pocket sweetheart…. If only! I would treat her like a princess, the beautiful woman she is.
Footballer arseholes like Rooney and Giggs are scumbags who view women as pay off sex dolls, Lampard’s turn in the scandal spotlight will come, and poor Chrissy will get hurt, poor babe.
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