TideLog Posts Tagged “B7R”

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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The following functions are handled by the chassis control unit (CIM) on Volvo’s B7R coach, B7RLE low entry city bus, and B9TL double decker bus. Any faults usually result in a CHECK lamp illumination or a warning icon illumination, accompanied with a “Check diagnostics for Chassis Control Unit at next stop” message in the driver infodisplay.

Brake lights

The control unit controls the body’s brake lamp with the help of a retarder signal and a brake lamp signal from the bus Vehicle Electronic Control Unit (VECU).

Idle

The chassis control unit’s idling function signals to the body when the accelerator pedal is in idling position.

Kneeling

The kneeling function works together with the electronically controlled suspension (ECS) and activates a lamp on the instrument panel when the bus kneels. The function also activates a CHECK warning when the ECS indicates that pressure is too low.

Buzzer

The buzzer function controls the external buzzer in the dashboard which is connected to the chassis control unit (CIM). The buzzer is activated on request from the body and from the internal CIM functions. The buzzer sounds when CHECK messages or other info is displayed in the instrument panel.

Check of battery voltage level

The function senses when the bus’s batteries (2x12v batteries, each with an alternator) voltage is less than 22 Volts and then shuts down all voltage users that have low priority. When battery voltage hits less than 16 Volts an internal signal is generated for low battery level, and with voltages exceeding 36 Volts an internal signal is generated for high battery level. These internal signals are used for opening and closing certain inputs and outputs. The signal for low battery level also closes the normal signal transmission on the J1587/J1708 link. Low battery voltage will result in erratic engine starting and other electrical failures.

Retarder control

In normal operation the retarder (engine brake, known as JAK, JaKob’s engine brake) will only accept a number of preset braking torques. In those cases when the vehicle control unit (VECU) wants the retarder to brake with a torque which is not preset, this limiting function must be disconnected. This is achieved by activating an earth signal on the retarder control unit’s inputs.

Brake pressure

The brake pressure function reads off the air pressure on the front and rear brake tanks respectively, and controls the corresponding gauge on the instrument panel via data link J1587/J1708. The function also activates an alarm on the instrument panel when insufficient pressure is shown.

Vehicle speed

The function gives three output signals when the vehicle’s speed exceeds 5 km/h, 20 km/h and 95 km/h. The function also controls a frequency-modified signal with constant pulse width which represents the vehicle’s speed. (This signal is known as the C3 signal.)

Starter motor

The chassis control unit checks that the requirements for starting are fulfilled and then activates the starter motor’s relay.

Dimmer

This function reproduces the rheostat level which is given from the instrument panel to be used in the body instrument’s lamps.

Parking brake

The parking brake function gives a signal indicating the parking brake’s status to the body system when the parking brake is engaged. The body system uses the status signal to activate an alarm if the door to the driver’s cab is open when the parking brake is disengaged. The chassis control unit (CIM) also activates the parking brake lamp on the driver’s instrument panel.

Fire alarm

If a fire is discovered in the engine bay or in the bus body, a fire alarm is activated on the instrument panel. The fire alarm also activates the instrument cluster buzzer.

Main switch

The vehicle’s main electrical circuit cannot be permitted to close down in an uncontrolled way, i.e immediately. After the ignition is switched off certain functions must be provided with power for a certain period of time. The gearbox takes ten seconds to close down, which is the longest closing-down time. For this reason, the chassis control unit’s holding circuit function releases the holding circuit ten seconds after the ignition has been switched off and leaves the switching off of the main circuit to the main circuit’s switch.

Steering wheel adjustment

This function checks that the parking brake is applied and that the ignition is on before it permits adjustment of the steering wheel and instrument panel.

Fuel level

The fuel level function receives signals from the fuel level sensors and controls the fuel level gauges on the driver’s instrument panel. The function also sends a warning to the instrument panel when insufficient fuel level is recorded.
The calculation of the fuel level is determined by how the jumpers are set, (so that the function can be adapted to different fuel tanks). In those cases in which there are two fuel tanks, the jumpers decide the relationship between the sizes of the tanks. If there is only one tank, the jumpers give the setting the shape of the tank. (The jumpers can only be set to 15 V, earth or not be connected at all).

Fuel cut-off

This function controls the fuel cut-off’s solenoid valve and retains its position until the valve needs closing. A pulse for closing the valve is sent when the emergency switch is activated or when the main switch is switched off. The valve is opened when the emergency switch is switched off and the main switch is active or if the main switch is activated while the emergency switch is switched off. If both are activated at the same time, the emergency circuit breaker overrides.

Bogie

The bogie function checks the air pressure in the bogie axle’s air suspension bellows and activates a lamp on the driver’s instrument panel when the air pressure is released. This funtion only applies to tri-axle B7R coaches with a double rear axle (bogie). Most B7RLE and B9TL doble deckers have one front and one rear axle. The inner-most axle of a bogie can be raised or lowered using the air suspension.

Alternator

The chassis control unit (CIM) senses the status of the alternators, illuminating icons on the instrument panel if any of the alternators are not charging. This warning is shown before the engine is started in order to ensure that the function works. If the alternator lights do not go out once the engine is running, check the alternator(s) drivebelt, or the regulators on the alternators for any faults. If the battery voltage in the infodisplay is less than 22v but the batteries are fine, there is a fault in one or more alternator regulators.

Engine start/stop

The chassis control unit (CIM) handles the start signal to the vehicle control unit (VECU) and checks that established requirements for starting are fulfilled.

Temperature

The temperature function reads from an inside sensor and an outside sensor and sends the signals to the instrument panel where the temperatures are shown on the infodisplay.

Gearbox

In those cases where the vehicle is equipped with MGS or EGS, the gear position function signals to the instrument panel if the gearbox is in high gear. The function also informs the instrument panel if the EGS gives a warning signal.

Open door

The open door function senses whether a door is open and, if so, lights up a symbol on the instrument panel, sounding the instrument cluster buzzer all the time the door is open. Once the open door is closed, the buzzer turns off. The open-door function is used with a conventional electrical system in the body. It monitors doors such as the emergency exits, cab door (not all bodies support this) and the bonnet. On some vehicles the passenger entry door is linked to this so the bus cannot be moved if it is open or has a faulty potentiometer.

On the B7RLE and B9TL, a faulty potentiometer or potentiometer track switch on the passenger door usually results in the STOPPING sign not extinguishing once the doors open. It should go out when the doors open, not when they close.

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As I mentioned in THIS PREVIOUS POST, the electronic accelerator pedal position sensor on Volvo’s B7R coach, B7RLE low entry city bus version and their B9TL double decker can go faulty. This will result in the Engine ECU reducing the engine speed to safe mode, or limp home mode. The sensor is actually a big potentiometer that is adjusted. The more you press the pedal, the resistance increases, so the engine ECU knows how much to increase engine speed, and as you’ll know from those radios and other goods that use pots for volume controls, they go bad after so long, and start to become intermittent.

The pedal potentiometer is connected to the Vehicle ECU (VECU). The VECU converts the resistance value from the potentiometer into a percentage value, and sends it to the Engine ECU, which in turn adjusts the engine speed by increasing air and fuel intake amongst other things, while sending data to the Transmission ECU (TECU) about the engine speed so it can adjust gears, or operate the retarder (engine brake) etc. As I mentioned in the other post, the accelerator pedal potentiometer 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 only allowing the bus to reach a certain speed, so that the vehicle can be moved (known as Limp-home). The digital (IVS) signal enters via a port in the VECU, which in turn is connected to the body contact block (BB1:1).

Here I’ll show you how to replace the potentiometer, as I did it a few days ago on my favourite B7RLE of Rikku’s fleet! The CHECK light came on with the “Check diagnostics for Engine ECU at next stop” message, it wasn’t accelerating smoothly. The turbo gauge wasn’t moving either, it all felt like the engine was in a deep sleep and didn’t want to move the bus!

As I discussed in my last article about the sensor, both pedal sensor and turbo failure can generate the same symptoms, causing limp home mode (Rikku calls it sleepy snail mode!) with the CHECK light and “Check Diagnostics for Engine ECU” message in the info panel. Thereby make sure you fully investigate all possible causes by reading ECU fault codes using VCADS Pro, and checking wiring.

Once you have verified the fault, and determined the pedal sensor is definitely at fault, it’s time to replace the sensor.

1. Remove the drivers seat. This isn’t ultimately necessary, but I found it made more workroom than just adjusting the seat as far back as its rails would allow. The removal of the seat depends on the seat itself, as different B7R’s and B7RLE’s have different seats, depending on the body and option configuration. If you’re not sure how to remove it, just make it go back as far as possible.

2. Make sure the engine is switched fully off, and that the ignition switch is in position 0. Disconnect the bus electrical system.

3. Locate the pedals (duh!), don’t forget that the right pedal is the accelerator pedal, the one we need! Remove the floor mat, or move it aside:

4. Remove the 3 bolts holding the pedal assembly to the bus floor, placing them safely aside, below is the location of the fixing bolts:

5. Move the accelerator pedal to the side and remove the cable clamp (1). Remove the connector (2). Remove the accelerator pedal sensor potentiometer screws (3) as numbered and shown below. Remove the sensor.

You shouldn’t need to remove the second cable mounting clamp with screw seen in the image, unless the sensor supply cable needs to be replaced. This runs under the bus chassis up to the Vehicle ECU, and is joined in various places depending on the bus, wiring and body, as the signals go from the VECU to the EECU and TECU.

6. Fit the new sensor, and mount it, making sure it fits back exactly in the same position as the old one, with the wiring connector facing downwards. Refit the pedal with the 3 bolts, and perform a hand test. Press the pedal with your hand and make sure it is smooth. Refit the floor carpet, and driver’s seat, if you completely removed it for workspace. If not simply slide it back into driving position and make sure the seat adjustment rails lock in place when the adjustment lever is released.

7. Switch the bus electrical system back on, start the engine, and perform a rev test with the gearbox in Park or Neutral (the B7R coach is manual, the B7RLE city bus version is often auto), pressing and releasing the pedal. Watch your revs and listen to the engine. If the CHECK light illuminates and/or any Check Diagnostics messages appear in the infodisplay, perform testing on other areas. There could be signal loss between control units and wiring.

8. Perform the VCADS-test: 27102–3 Accelerator pedal, test with your diagnostic PC connected to the electrical system of the bus.

9. If the standstill rev test and VCADS tests were successful, take the bus for a test drive, varying your pressure on the pedal. When I’m on a test track I like to thrust the pedal up and down to make sure the system and engine reacts, being gentle then rough, but DO NOT do this on public roads!

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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.

Purpose

The electronic accelerator system allows the driver to provide manual control of the engine speed, and thereby the speed of the vehicle.

Variant differences

  • 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.

Requirements

  • 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

Function

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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