Here is some useful information about the EVO Steering system used in our Tahoe's and Suburban’s.
This system was used from 1997 until 2000 and abandon by GM partially because of problems mostly with inconsistent steering and possible legal ramifications (I have been told it was also on a handful of very late production 1996's)
First, it is called Electronic Variable Orifice Steering and works like this:
The computer monitors vehicle speed and steering wheel action to activate/deactivate a solenoid on the power steering pump. This solenoid opens and closes to control the fluid flowing to the steering gear.
At low speeds the solenoid open fully allowing full pump pressure to the steering box thus giving the operator easy steering. At higher speeds the solenoid operates and closes to restrict the fluid flow stiffening the steering. (so, power to the evo is removed at low speeds and provided at high speeds to activate the solenoid)
This system uses the steering sensor to determine the position and speed of movement of the steering wheel and uses this to determine when the EVO solenoid will open and restrict.
Troubleshooting the system:It's really easy if you own a GM Tech 2 tool, but since most of us don't here are a few things you can try:
Jerky Steering:Unplug the (red) plug on the bottom of the EVO solenoid, this is located on the power steering pump and can be accessed from the bottom of the vehicle. Once unplugged the pump will be applying full pressure to the steering gear and you should have very easy steering that will not change with vehicle speed or wheel position. If this solved the wheel jerking replace the wheel position sensor.
I know of a few people that just left the EVO solenoid unplugged to resolve the jerky steering. Though it does solve the problem it creates a new and more dangerous one: over steering and sensitive steering at high speeds, not recommended! Fix the problem or delete the system!
EVO Delete:Knowing the error of their ways GM made a kit to delete the EVO system completely, what they did was to remove the EVO solenoid from the rear of the power steering pump and added an adapter that would allow the existing high pressure hose to be connected to the back of the pump. The part no for this kit is: 19168825 and sells upwards for about $60.00. It comes with a new power steering union and hose adapter. If you do this keep in mind you will have standard steering effort at all speeds, some really like this because it gives more of a sporty feel. The downside is your wife will probably bitch about the harder steering.
Another way to delete the EVO system (and much more cost effective) is to simply go to your local junk yard, find a pre-97 and remove the union from the pumps high pressure line, if the pressure line is in good shape take it to. These parts should cost less than 10 bucks. If the hose is shot get a new one at your local parts store, ask for a 1995 Tahoe high pressure hose. Remove the EVO solenoid from the rear of the pump , remove the high pressure hose install your replacement parts. With the car jacked up and not running operating the steering stop to stop at least 10 times, add fluid to the pumps reservoir as needed and your done!
Replacing the steering sensor: There are lots of good write-ups on the replacement of the wheel sensor so I won't go into that, one thing to mention, make sure the new sensor goes in exactly as the old one was removed, look at the old one, clock the new one exactly as the old and insert as it was removed.
One last thing, the 4x4 Tahoe, Suburban uses a 16:13:1 variable ratio steering gear (25001484). If your box is shot make sure you get the same part number, many rebuilder will give you 25001843, this is a light duty 2WD unit. It will fit but your steering will change, the zero position will also be off and will require a front end alignment to correct your steering wheel position.
Helpful Part numbers:
Wheel Sensor: Dorman Part# 31025, GM Part no:26064468
GM EVO Delete kit:26064468
Steering Gear:25001484
Happy wrenching!
Dan
This system was used from 1997 until 2000 and abandon by GM partially because of problems mostly with inconsistent steering and possible legal ramifications (I have been told it was also on a handful of very late production 1996's)
First, it is called Electronic Variable Orifice Steering and works like this:
The computer monitors vehicle speed and steering wheel action to activate/deactivate a solenoid on the power steering pump. This solenoid opens and closes to control the fluid flowing to the steering gear.
At low speeds the solenoid open fully allowing full pump pressure to the steering box thus giving the operator easy steering. At higher speeds the solenoid operates and closes to restrict the fluid flow stiffening the steering. (so, power to the evo is removed at low speeds and provided at high speeds to activate the solenoid)
This system uses the steering sensor to determine the position and speed of movement of the steering wheel and uses this to determine when the EVO solenoid will open and restrict.
Troubleshooting the system:It's really easy if you own a GM Tech 2 tool, but since most of us don't here are a few things you can try:
Jerky Steering:Unplug the (red) plug on the bottom of the EVO solenoid, this is located on the power steering pump and can be accessed from the bottom of the vehicle. Once unplugged the pump will be applying full pressure to the steering gear and you should have very easy steering that will not change with vehicle speed or wheel position. If this solved the wheel jerking replace the wheel position sensor.
I know of a few people that just left the EVO solenoid unplugged to resolve the jerky steering. Though it does solve the problem it creates a new and more dangerous one: over steering and sensitive steering at high speeds, not recommended! Fix the problem or delete the system!
EVO Delete:Knowing the error of their ways GM made a kit to delete the EVO system completely, what they did was to remove the EVO solenoid from the rear of the power steering pump and added an adapter that would allow the existing high pressure hose to be connected to the back of the pump. The part no for this kit is: 19168825 and sells upwards for about $60.00. It comes with a new power steering union and hose adapter. If you do this keep in mind you will have standard steering effort at all speeds, some really like this because it gives more of a sporty feel. The downside is your wife will probably bitch about the harder steering.
Another way to delete the EVO system (and much more cost effective) is to simply go to your local junk yard, find a pre-97 and remove the union from the pumps high pressure line, if the pressure line is in good shape take it to. These parts should cost less than 10 bucks. If the hose is shot get a new one at your local parts store, ask for a 1995 Tahoe high pressure hose. Remove the EVO solenoid from the rear of the pump , remove the high pressure hose install your replacement parts. With the car jacked up and not running operating the steering stop to stop at least 10 times, add fluid to the pumps reservoir as needed and your done!
Replacing the steering sensor: There are lots of good write-ups on the replacement of the wheel sensor so I won't go into that, one thing to mention, make sure the new sensor goes in exactly as the old one was removed, look at the old one, clock the new one exactly as the old and insert as it was removed.
One last thing, the 4x4 Tahoe, Suburban uses a 16:13:1 variable ratio steering gear (25001484). If your box is shot make sure you get the same part number, many rebuilder will give you 25001843, this is a light duty 2WD unit. It will fit but your steering will change, the zero position will also be off and will require a front end alignment to correct your steering wheel position.
Helpful Part numbers:
Wheel Sensor: Dorman Part# 31025, GM Part no:26064468
GM EVO Delete kit:26064468
Steering Gear:25001484
Happy wrenching!
Dan
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