TideLog Posts Tagged “EMS2”

In this article I’ll show you what all the dials and indicators mean in the instrument cluster of Volvo’s EMS (Electronic Multiplex System) v2.0, the symbols, and what they mean. This dash is not just used on Volvo’s B7RLE/B7/9TL buses, it is also used on their range of coaches too, there may be differences, but the specifics are here. Their FH & FM range of trucks have the same indicators and dials, but the cluster layout is different.

A. Oil pressure gauge, engine

This gauge indicates the current engine oil pressure. The needle must not enter the red zone when the vehicle is being driven! This can sometimes be unavoidable on very hot days, but if it does, lower your revs as much as possible to lower the pressure and thus the temperature. The engine can be seriously damaged if oil pressure is lost due to an oil leak for example. This gauge gives a reading when the ignition key is in the drive position.

The LED in the lower left-hand corner lights when the engine control unit sends a low oil pressure signal, no matter what the gauge reads. The STOP exclamation indicator will light if the oil level becomes too low due to a leak, if it does, stop the bus and have it checked. If the bus is driven with a leak and the oil runs out, serious engine seizure and damage will result.

B. Temperature gauge, coolant

This gauge shows the engine coolant temperature. The same procedure above as for the engine oil should be followed.

C. Turbo pressure (boost) gauge

This needle shows how much boost the turbo is giving. Generally it will be higher under heavy acceleration and on hills, but you should not stress it too much otherwise the engine may go into limp home mode, shutting the turbocharger off to protect it from overheating.

D. Display (Infopanel)

This is where everything is displayed. Trip measurement, fuel economy, time/date. It also displays “Check diagnostics for xxx ECU” messages, along with the CHECK light (see J.). Failure icons and messages are also displayed, along with the STOP exclamation triangle (See I.). Info messages are also displayed, with the INFO indicator (See K.)

E. Tachometer

The tachometer displays the current engine speed in revolutions per minute (RPM) from 500 revs to 3,000 revolutions. Engine tickover (idle) speed is around 650rpm, and optimal gear upshift/downshift revs are between 1,000 and 2,000 revs. As always, observe the safety colur band in the rev ranges, and do not go over the yellow range maximum, otherwise engine damage will result.

F. Speedometer

The speedometer (speedo for short) displays the current total vehicle speed in km/h, some UK vehicles have it in mp/h, don’t get the two confused!

G. Fuel gauge

This gauge shows how much fuel you have left in the tank. This relates to single diesel tank fitted buses and trucks. For biodiesel and adblue vehicles, and Volvo vehicles fitted with dual diesel tanks there may be another separate dial. For adblue and biodiesel these are not normally Volvo fitted, but fitted by the body manufacturer or retrofit company to customer order (for buses) or the fleet company (for trucks). For information consult your vehicle documentation or builder.

H. Brake pressure gauges

These dials show the air pressure in the brake cylinders of the system. The pressure must not be allowed to get too low, otherwise brake failure will result. If it gets too low or high a Check Diagnostics warning is displayed in the Infopanel display, and a failure of the system will normally result in the STOP exclamation indicator coming on, in which case the vehicle MUST NOT be driven any further. Damage to the vehicle, other road users, passengers and yourself will result.

I. STOP exclamation indicator

This indicator will illuminate if a CRITICAL failure or other critical event happens, such as engine oil, coolant and/or fuel getting too low, an ECU or CAN/J1939 communications bus failure on the multiplex controller area network electrical system, brake failure, engine failure. If this indicator illuminates, STOP THE BUS IMMEDIATELY and have the cause rectified by an engineer. They, like myself, have the tools, knowledge and software to determine the cause by communicating with the vehicle electrical computer systems to find fault codes that tell us exactly where the fault is.

You MUST get the vehicle towed if this light comes on, for utmost safety. If you’re carrying passengers, make sure they are your first priority. Shut off the engine and use the emergency cutoff switch in the cab if you are worried about fuel or electrical fires or problems, it cuts both off safely. You’d be putting passengers, yourself and road users in extreme danger by driving a possibly seriously faulty vehicle that weighs over 18 – 30 tons by thinking the indicator is coming on for nothing, this is rarely the case. Volvo multiplex systems and control units are very very accurate. I can’t stress it enough.

J. CHECK warning indicator

This indicator comes on when there is a warning condition in one or more electronic control units (ECU’s) in the bus. They are not extreme failures, just friendly warnings that a service is needed. It will illuminate along with the following messages displayed in the Infopanel display:

1. “Check Diagnostics for Brake ECU at next stop”

This is the most common one you’ll see, and it means the brake wear sensors have detected the pads or discs are nearing their wear limit. It will also trigger when slight drops in pressure or leaks occur on the brake air system. Drops in pressure can be determined by ear. Listen to the discharge pattern when the system lets off steam regularly. The system discharges in two stages, two hisses about 2 seconds apart, every 5 or so minutes. If they are too long, too regular, the pressure may need to be looked at. Determine this by reading the pressure gauge in the dash as earlier in the article.

2. “Check Diagnostics for Engine ECU at next stop”

This message appears when a warning is triggered from the engine’s ECU. Situations include engine temperature sensor failure (look for the oil temp needle being cold when it shouldn’t), engine coolant sensor failure, tachograph sensor failure (for detecting RPM’s) and various others.

3. “Check Diagnostics for Light Control Unit at next stop”

The Light Control Unit controls all vehicle illumination and signalling equipment. Headlights, tail lights, indicators and brake lights. On buses it also controls gangway lighting, as they are wired into the main lighting system along with the destination board, normally wired in with the running lights (sidelights). The Light ECU monitors resistance across all lighting circuits, and any failing bulbs or LED brake/indicator clusters (used on Volvo buses with Wright Eclipse Urban/Gemini bodies) cause high resistance, so the ECU knows a light circuit has failed.

I am unaware if the Light ECU can trigger the STOP indicator.

K. INFO indicator (Can illuminate in conjunction with CHECK indicator)

This light comes on when the Infodisplay is set to Info messages in the display, such as fuel consumption etc, and a CHECK warning is displayed. Switch the display over using the control stalk on the steering column to view any CHECK messages and the INFO light will extinguish.

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If you’re driving along and suddenly the “Check Diagnostics for Engine ECU at next stop” message appears in the dash infopanel, along with the CHECK indicator and the temperature gauge reading cold or just above cold, the engine temperature sensor has failed or is dirty and will need to be replaced.

Units Involved

The Engine ECU (EECU) and the Vehicle ECU (VECU) are involved in this process. The Engine ECU periodically checks the temperature sensor. The resistance readings are sent as a changing signal to the dash temperature tacho needle as the temperature decreases or increases, the signal power varies the needle position. After 5 or 10 minutes from cold start the engine ECU knows that the engine should be warm, so if it starts to get a completely cold reading after this time, sends a signal via the CAN (Controller Area Network) to the VECU which displays a message in the dash infopanel.

Cause Elimination

This fault should not be deemed to be the temperature sensor if only the temp needle is too low. The CHECK light and message MUST also be displayed. Otherwise, the tacho needle must be checked, and/or the signal from the VECU.

To check if the needle is faulty, turn off the bus engine and ignition completely, turning the starter to 0. Turn it to I to switch on the ignition and the needles should all do a full sweep of their dials to the right then return back to the left. Turning the starter to II will start the engine, all fuel and air dials should go to their operating positions, showing the correct fuel and air pressures. To check the turbocharger boost needle you will need to drive the bus on hard acceleration on a straight road. It will not move if the footbrake or airbrake is applied as the turbo only operates when the bus is moving in gear.

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