Cooling System - Electro-Viscous Fan Clutch Operation
Information IB06-01-S001Operating Characteristics Of The Electro-Viscous (EV) Fan Clutch
And Diagnostic Tips For Cooling Fan Noise, Delayed
Transmission Shifts And/Or Engine Revving Too High
ISSUE DATE: APRIL 2006
Affected Vehicles
2003-2006 Isuzu Ascender (US/UT)
Service Information
Vehicles built after the Date listed in the table are equipped with the new electro-viscous (EV) fan clutch:
The updated design of the electro-viscous (EV) fan clutch helps improve A/C performance but may also experience higher fan engagement noise and produce some erroneous symptoms which include delayed transmission shifts, or engine rewing too high.
This new design EV fan clutch has been installed on production vehicles from the end of 2005 model year production (June 2005) and all 2006 model year vehicles. The new design EV fan clutch may also be present on vehicles serviced with this new part per Bulletin Number SB05-12-S002 or for other service related conditions.
IMPORTANT:
Unless a specific issue is identified by proper Service Manual diagnosis; DO NOT replace the fan clutch for fan noise.
DO NOT replace an EV fan clutch unless a specific condition related to the EV fan clutch is identified using the Service Manual diagnostics. If the fan has a condition that warrants replacement, a DTC should set and/or the Service Manual diagnostics should lead to the replacement of the fan clutch.
If the fan is not operating at the proper speed/function, the appropriate diagnostic trouble code should set. Identify the root cause of the condition. Please make sure to do a thorough review of the Service Manual for proper diagnostics. Service Bulletins are available regarding the EV fan.
Refer to "Operating Characteristics" and "Diagnostic Tips" in this bulletin for additional information.
OPERATING CHARACTERISTICS OF THE ELECTRO-VISCOUS
(EV) FAN CLUTCH
Changes to the EV fan clutch to improve the HVAC performance basically increase airflow in certain conditions. It is now possible during start up for the EV fan clutch to be engaged and match engine speed for about 1 minute depending on driving speeds (with lower speeds having a longer disengagement time) producing some noise/flare. The noise/flare will most likely be intermittent and can be dependent on the following conditions:
^ Fan clutch valve orientation, with the check ball at 11:00 position as viewed from front of vehicle when the engine is stopped.
^ HVAC or powertrain cooling conditions when the vehicle is shut off.
^ Parking incline - vehicles parked nose up on a 16% or higher incline (such as vehicles coming off transport or parked on steep driveways) may have prolonged fan noise/flare until the fluid is pumped out of the working chamber of the fan. These conditions can occur in as little as ten minutes. Once the vehicle is not parked in these conditions, it should operate as expected.
^ If the vehicle is parked nose down with a 16% or more decline, the EV fan clutch may have a delayed engagement response similar to what is described in Bulletin Number SB05-12-S002.
IMPORTANT:
DO NOT replace EV fan clutches for the conditions listed above; they are expected vehicle characteristics. If the fan clutch is truly operating at a speed higher than intended, a DTC P0495 or P1484 should set. Additional codes are available for other conditions.
DIAGNOSTIC TIPS
Depending on the vehicle year, the Tech 2 may allow some EV fan control using the special functions application of the Tech 2 (refer to the proper Service Manual). If this function or a fused jumper wire is being used to check EV fan response, there may be a delay in fan response (up to 2-3 minutes depending on conditions, please refer to the Service Manual diagnostics).
The desired fan speed and actual fan speed data (on the Tech 2) can be misleading. The desired fan speed is comprised of the maximum of multiple parameters (for example engine coolant temp, NC pressure, etc.) and may not be the ruling desired fan speed parameter. The end result may be that the actual desired fan speed is lower than what is displayed. Additionally, the desired fan speed may be higher than the current engine speed. The fan is limited by the current engine RPM and will max out at about 3500 RPM under full manual fan engagement request along with a corresponding engine RPM speed. The 4.2L 1-6 engine's desired and actual fan speeds will usually be closer to each other than the 5.3L V-8.
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