P38a EAS System Data

P38a EAS - Air Dryer


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The EAS Dryer is an essential and often overlooked EAS component. The primary function of the EAS dryer is to absorb moisture from the compressed air in the EAS system. A potentially bad situation could arrise if moisture contained within the compressed air froze or corroded metalic components. This is not a huge issue for drier climates but the vehicle was designed in the United Kingdom and I hear it gets wet there sometimes.

The EAS Dryer is connected to the high pressure tank through a Non-return check valve and the oring fittings should be checked when hunting down slow leaks.

 


P38a EAS - Front Air Spring

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The EAS suspension uses bladders of air to act as the cushion between the axle and the body of the vehicle. These bags can be inflated or deflated depending on the height set by the operator of the vehicle. Solenoids driven by the EAS ECU control air pressure either into or out of each corner of the vehicle. Thereby controling the ride height and comfort of the driving experience.

Sounds like a nice design, right? Well it is when it works. In my opinion the air springs are critical to the overall operation of the EAS. If the springs are cheap or in disrepair, the EAS system suffers and annoys the heck out of the vehicle operator. From my experience old or cheap bags are the cause of most EAS air leaks.

The OEM Rover airspring can be a troublesome beast. The OEM design employs a beaded rubber junction between the top and bottom pieces of the air spring unit. This beaded design is similar to how an automotive tire is mated to the wheel rim. During extreme articulation, the bead can seperate from the bottom or top piece of the air spring. This can reult in a very loud bang or maybe just a moderate escape of pressure. Either way the bead must be reseated and hope you avoid an EAS Fault. There is also some debate as to whether the OEM air space design is backwards in firming up or softening the ride.

The OEM bags and in fact all bags can eventually develop cracks and dry points in the rubber. Depending on the design, these cracks can create uneven or broken sealing surfaces. These dry spots and cracks cause leaks. Leaks eventualy cause EAS Faults.

The above picture displays a set of Arnott Generation III airsprings. In my opinion, these are the only replacement air springs that a Rover owner should consider. I tried every one of Arnott's different generation air springs and was only happy with the GENIII design. Every owner should just write off the cost and committ to getting the GENIII bags.

The Arnott GENIII air springs are avalaible through Rover Renovations.

 


P38a EAS - Valve Block and Pump


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The EAS pump and block assembly are located under the hood contained within a plastic enclosure marked "EAS". The pump is a high pressure low volume reciprocating piston pump. The pump is driven by a low voltage/current logic signal from the EAS ECU which triggers a Relay in the Main Fuse Box. The EAS pump also has a built in overtemp sensor that signals back to the EAS ECU. Pressure generated from the EAS Pump is fed into the EAS high pressure tank. Typically the most common failure point on these pumps is the piston seal. Replacement piston seals can be purchased from Rover Renovations.

The block assembly primarily conatins the solenoids used to actuate air pressure to the various suspension bags. Solenoids can occasionally fail but more than likely the entire valve block assembly might need a rebuild. The rebuild involves various orings and rubber gaskets. Again this is the realm of Rover Renovations.

The valve block assembly also contains what is know as the EAS Driver Module. This module is a black plastic enclosure that is tucked away under the valve block. The EAS Driver, receives low voltage signals from the EAS ECU and converts this logic signal to a PWM modulated 12v DC signal. The Solenoids are not simply driven by on and off 12v supply but rather a fancy start up and sustain PWM signal. One should never drive the solenoids straight off of a 12v supply.

 


P38a EAS - Main Fuse Box

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The fusebox is a sometimes troublesome aspect of the Range Rover. I as a rule, carry duplicate green and yellow relays in my glove box. These relays are prone to failure when exposed to high heat or when under continous load.

The fusebox is also located in close proximity to the Engine Coolant resovior. This has been know to cause corrosion problems with the interior of the fusebox. One might think that the fusebox is a simple PCB board with sockets for each of the relayes and fuses. Well one would be very wrong. The fusebox is an insanely complex double board design that in my opinion is unserviceable.


P38a EAS - Electronic Control Unit

 


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Here we come to my favorite part of the Range Rover EAS. The EAS Electronic Control Unit (ECU) is a very elegant and highly efficient microprocessor driven sub-system. The EAS ECU performs all of the logic processing and logic signaling for the EAS operation. The ECU monitors all four EAS sensors and periodically makes adjustments to the suspension height. The ECU also monitors any user input from the EAS buttons and changes the suspension height accordingly. The EAS pump and each of the solenoid air valves are also driven by the EAS logic signaling. All of this comes together to create the sometimes interesting behaviors of the EAS.

At the heart of the ECU is a Motorola 68HC05 series microcontroller. This microprocessor is surrounded by a huge array of voltage shifting, inverting and conditioning circuitry. There is an extremely abundant collection of information about the Motorola 68HC05 processor avaliable on the web. It was these documents that allowed me to create a best guess about the EAS serial physical layer communications protocol.

 

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The unit is extremely durable and rugged. I have heard of people manually hooking up the voltages accidentally in reverse with no adverse affects. Although I would not recomend this.

The Massive multiplug that connects the EAS ECU to all the various suspension components is labeled as Connector C117. The function of each connector on the C117 multiplug is listed below:

 

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P38a EAS - Front Sensor Arm


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The EAS suspension relies almost entirely on the height sensors for empirical data on the outside world. These sensors are a feedback for several assumptions that the EAS ECU makes on the condition of the suspension system. Any failure of a sensor will trigger an EAS Fault.

The EAS height sensor is a Potentiometer fed with a regulated 5v reference signal. This reference voltage is then modified by the resistive Potentiometer and a voltage is fed back into the EAS ECU. The modified voltage is then fed into one of the A2D converters on the Motorola 68HC05 microprocessor. The 0-255 Digital value of the sensor voltage is then used to determine the exact position of that sensor and the height of the suspension.

The potentiometer inside the EAS height sensor can develop dead spots over time. These dead zones result in an inaccurate or a nonresponsive reading back to the EAS ECU. If the ECU tries to raise a corner of the vehicle and there is not a corresponding change in the height sensor then an EAS fault can be logged. The EAS ECU has different fault codes for a sensor that has bad reading versus an EAS sensor that is completely disconnected.


P38a EAS - Rear Sensor Arm


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The EAS suspension relies almost entirely on the height sensors for empirical data on the outside world. These sensors are a feedback for several assumptions that the EAS ECU makes on the condition of the suspension system. Any failure of a sensor will trigger an EAS Fault.

The EAS height sensor is a Potentiometer fed with a regulated 5v reference signal. This reference voltage is then modified by the resistive Potentiometer and a voltage is fed back into the EAS ECU. The modified voltage is then fed into one of the A2D converters on the Motorola 68HC05 microprocessor. The 0-255 Digital value of the sensor voltage is then used to determine the exact position of that sensor and the height of the suspension.

The potentiometer inside the EAS height sensor can develop dead spots over time. These dead zones result in an inaccurate or a nonresponsive reading back to the EAS ECU. If the ECU tries to raise a corner of the vehicle and there is not a corresponding change in the height sensor then an EAS fault can be logged. The EAS ECU has different fault codes for a sensor that has bad reading versus an EAS sensor that is completely disconnected.


P38a EAS - Rear Air Spring

 


eas_rearspring_front

eas_rearspring_scaled

 

 

The EAS suspension uses bladders of air to act as the cushion between the axle and the body of the vehicle. These bags can be inflated or deflated depending on the height set by the operator of the vehicle. Solenoids driven by the EAS ECU control air pressure either into or out of each corner of the vehicle. Thereby controling the ride height and comfort of the driving experience.

Sounds like a nice design, right? Well it is when it works. In my opinion the air springs are critical to the overall operation of the EAS. If the springs are cheap or in disrepair, the EAS system suffers and annoys the heck out of the vehicle operator. From my experience old or cheap bags are the cause of most EAS air leaks.

The OEM Rover airspring can be a troublesome beast. The OEM design employs a beaded rubber junction between the top and bottom pieces of the air spring unit. This beaded design is similar to how an automotive tire is mated to the wheel rim. During extreme articulation, the bead can seperate from the bottom or top piece of the air spring. This can reult in a very loud bang or maybe just a moderate escape of pressure. Either way the bead must be reseated and hope you avoid an EAS Fault. There is also some debate as to whether the OEM air space design is backwards in firming up or softening the ride.

The OEM bags and in fact all bags can eventually develop cracks and dry points in the rubber. Depending on the design, these cracks can create uneven or broken sealing surfaces. These dry spots and cracks cause leaks. Leaks eventualy cause EAS Faults.

The above picture displays a set of Arnott Generation III airsprings. In my opinion, these are the only replacement air springs that a Rover owner should consider. I tried every one of Arnott's different generation air springs and was only happy with the GENIII design. Every owner should just write off the cost and committ to getting the GENIII bags.

The Arnott GENIII air springs are avalaible through Rover Renovations.


P38a EAS - High Pressure Resovior


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The high pressure EAS tank is located under the frame rail just forward of the Range Rover fuel tank. This resovior holds approximately 2.5 US gallons(9.7L) of compressed air at 150 PSI(10 bar). The pressure contained within this tank should not be treated lightly and the utmost care should be used when interacting with this system.



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