QuestionThank you John. I must have had my foot on the brake pedal else how did I get OUT of park mode again??? Also the rattling type noise I heard only occured during the 5 seconds travelling in Park Mode at about 10mph and I was wondering whether perhaps the transmission would simply not go into Park as the vehicle was not going slow enough? (as is the case with reverse) Thanks again.
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-----Question-----
My Discovery was put into Park mode by mistake whilst travelling at about 10mph. This caused a rattling sound and a slight burning smell but the vehicle did not grind to a halt as I would have expected it to. There appears to be no damage but did the transmission suffer as a result?
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Hi Chris,
yes but not sure where. You should have both the transmission and the transfer gearbox examined to determine the extent of the damage.
The rattle noise may be a gear tooth and the burning could be within the TG. Have it drained and inspected for metal fragments.
If it was me, I'd drain both the tranny and the TG and see what comes out. IF you see metal fragments then inspect deeper.
Best of luck,
JohnMc
AnswerHi Chris,
thanks for the kind words. The rattle is what makes me nervous and suspect a potential mechanical problem. You've got to determine if there is any serious damage. Perhaps it's just some wear on the gears or bearing.
I don't think the park/neutral switch was affected. More likely it would be the park lock gear within the transmission. Perhaps just a tooth is worn. Inspection is the only recourse.
Here's something that may clarify how your tranny functions:
+AUTOMATIC GEARBOX - ZF4HP22 - 24, DESCRIPTION AND OPERATION, Control schematic.
When the ignition is switched on, a bulb check is performed on the transmission temperature warning lamp and the mode warning lamps by the instrument pack and the EAT ECU respectively. The warning lamps are illuminated for approximately 3 seconds and then extinguished.
The gear position switch outputs are monitored by the BCU and the EAT ECU. The BCU outputs gear position signals to illuminate the position indicators each side of the gear selector lever and on the odometer LCD in the instrument pack.
In D, 3, 2, and 1, the EAT ECU outputs control signals to the gearbox to select the required gear.
In D, all forward gears are available for selection by the EAT ECU. In 3, 2 and 1, a corresponding limit is imposed on the highest gear available for selection. When R is selected, reverse gear only engages if the vehicle is tationary or moving at 5 mph (8 km/h) or less. When R is deselected, reverse gear only disengages if the vehicle is moving at 4 mph (6 km/h) or less.
Selector lever interlock (where fitted):
The interlock solenoid on the selector lever is de-energised unless the foot brake is applied while the ignition is on.
While de-energised, the interlock solenoid allows the elector lever to move through the range unless P is selected.
On entering the P position, the interlock solenoid engages a latch which locks the selector lever. When the ignition is on and the foot brake is applied, the BCU energises the interlock solenoid, which disengages the latch and allows the selector lever to be moved out of P.
Shift control
To provide the different driving characteristics for each mode of operation, the EAT ECU incorporates different shift maps of throttle position/engine speed. Base shift points are derived from the appropriate shift map. When a shift is required, the EAT ECU sends a request to the ECM for a reduction in engine torque, in order to produce a smoother shift. The percentage of torque reduction requested varies according to the operating conditions at the time of the request. When the EAT ECU receives confirmation of the torque reduction from the ECM, it then signals the shift solenoid valves in the gearbox to produce the shift. To further improve shift quality, the EAT ECU also signals the pressure regulating solenoid valve to modulate the hydraulic pressure and so control the rate of engagement and disengagement of the brake clutches.
I hope this helps a bit...
Regards,
JohnMc
