Bemble
Well-Known Member
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There have been so many posts about DTCs related to the inhibitor/gear position switch on the 6HP26 transmissions recently, that I thought I would try a quick and dirty test to see if I could measure the switch in operation just using tools many people already have lying around the workshop – in this case a multimeter and a 5V power supply.
Background
The earlier 5-speed transmissions used sliding contact rotary switches to provide the L1/L2/L3/L4 signals, the logic from which allowed the controller to determine the position of the selector shaft, and hence which gear position was selected (P, R, N or D). The GM 5L40-E switch was mounted internally and the ZF 5HP24 switch externally. In general, the GM switch proved to be very reliable, seldom giving problems. The ZF switch, on the other hand, was, and continues to be, somewhat unreliable judging by the number of posts on here with P0705 issues.
6HP26
ZF made big design changes for the 6-speed transmission which was introduced in 2006MY for petrol/gas engines and 2007MY for diesels. This transmission introduced the ‘Mechatronic’ unit which meant that the transmission controller was now mounted in the transmission’s sump rather than on the vehicle. At the same time, a new inhibitor/gear position switch was introduced which used a slider with four strips of magnets embedded in it and the position of the slider was determined by a set of four hall effect sensors, mounted on a PCB. Each magnet strip lined up with one of the hall sensors producing the L1/L2/L3/L4 signals for the controller to establish the slide position and hence the gear that had been selected. Importantly this was ‘non-contact’ switch and mounted in the sump, so reliability should be improved.
Starting with the mechanical layout of the manual valve (ZF call it Wählschieber, abbreviated to W-S) it’s a simple process to move this within its bore and identify the transition from Park (where the main pressure is trapped between lands and can’t go anywhere) to Reverse (where the mains pressure is directed to the SV-2 and KV-B valves, to activate the B & D clutches), then back to Neutral (where, once again, the mains pressure is trapped) and finally to Drive (where the mains pressure is directed to KV-A, KV-B, KV-C & KV-E).
The four positions are shown below. There is a small range of movement for each position.
Next, after connecting the slider containing the four strips of magnets to the manual valve in the same way it is mounted in the vehicle
each of the Hall sensors can, in turn, be measured with the multimeter to determine the ‘on’ and ‘off’ positions
(I’ve placed an actual size photo of the Hall sensor circuit board in its correct location in the above image, just to show its position)
Note that each Hall sensor will switch on and off several times during the full stroke of the slider. This is the result:
We can then place bands across these ‘on’ and ‘off’ positions which represent a unique sequence for L1, L2, L3 & L4
For example, if we say ‘on’ is 1 and ‘off’ is 0 then:
Park = 1,1,0,1
Reverse = 1,1,1,0
Neutral = 1,0,1,1
This logic is what the controller uses to determine the position of the slider, and therefore the gear position selected by the driver. Note that the D position has several bands i.e. 0,0,0,1 and 0,0,1,0 and 0,1,0,0 and 1,0,0,0. Presumably this is because some car manufacturers still use the gear lever to select lower gears manually and these bands represent (say) gears 5, 4 and 3.
Although this technique can be used to confirm if there’s an issue with the gear position switch, fixing it is quite a different problem. First of all, the PCB with the four Hall sensors mounted on it is embedded in potting compound and it looks like it would be an absolute nightmare to dig the circuit board out of the potting compound and resolder the connections, to replace it. I’d be very interested to hear if anyone has tried this, and how successful it was.
Regarding replacing the complete switch assembly (which would include the input speed sensor) I’m not aware of anyone who can supply new switches. I’ve seen plenty for sale for the Continental/Siemens module with the ribbon cable, used in the 6HP28 (see below) but none for the Bosch modules with the spot-welded conducting bars. Clearly, though, used ones are available.
6HP28
There are also an increasing number of posts on the forum regarding the unreliability of the inhibitor/gear position switch for the ZF 6HP28 transmission used in the 5.0 naturally aspirated and supercharged versions of the L322. Although the 6HP28 did include some uprated parts to increase its torque capacity, the main difference between it and the 6HP26 was the Mechatronic unit which had been redesigned to massively speed up the gearshifts. ZF changed manufacturers for the electronic module from Bosch to Continental/Siemens, at least for Range Rovers up to VIN DA765413. From VIN DA765414 they reverted back to Bosch Mechatronic units, although there can’t have been many of these 2013MY vehicles produced. The electronic module design for the Continental unit is quite different to the Bosch one, for which all the connections were made by metal connecting bars joined with spot welds, as the Continental units use a ribbon cable to provide all the electrical connections.
The inhibitor/gear position switch is also different, with a different PCB on which the Hall sensors are mounted. It’s a little more challenging due to access to the connections but my plan is to test a Continental/Siemens switch as well, to see if there are any differences to the Bosch switch.
Phil
Background
The earlier 5-speed transmissions used sliding contact rotary switches to provide the L1/L2/L3/L4 signals, the logic from which allowed the controller to determine the position of the selector shaft, and hence which gear position was selected (P, R, N or D). The GM 5L40-E switch was mounted internally and the ZF 5HP24 switch externally. In general, the GM switch proved to be very reliable, seldom giving problems. The ZF switch, on the other hand, was, and continues to be, somewhat unreliable judging by the number of posts on here with P0705 issues.
6HP26
ZF made big design changes for the 6-speed transmission which was introduced in 2006MY for petrol/gas engines and 2007MY for diesels. This transmission introduced the ‘Mechatronic’ unit which meant that the transmission controller was now mounted in the transmission’s sump rather than on the vehicle. At the same time, a new inhibitor/gear position switch was introduced which used a slider with four strips of magnets embedded in it and the position of the slider was determined by a set of four hall effect sensors, mounted on a PCB. Each magnet strip lined up with one of the hall sensors producing the L1/L2/L3/L4 signals for the controller to establish the slide position and hence the gear that had been selected. Importantly this was ‘non-contact’ switch and mounted in the sump, so reliability should be improved.
Starting with the mechanical layout of the manual valve (ZF call it Wählschieber, abbreviated to W-S) it’s a simple process to move this within its bore and identify the transition from Park (where the main pressure is trapped between lands and can’t go anywhere) to Reverse (where the mains pressure is directed to the SV-2 and KV-B valves, to activate the B & D clutches), then back to Neutral (where, once again, the mains pressure is trapped) and finally to Drive (where the mains pressure is directed to KV-A, KV-B, KV-C & KV-E).
The four positions are shown below. There is a small range of movement for each position.
Next, after connecting the slider containing the four strips of magnets to the manual valve in the same way it is mounted in the vehicle
each of the Hall sensors can, in turn, be measured with the multimeter to determine the ‘on’ and ‘off’ positions
(I’ve placed an actual size photo of the Hall sensor circuit board in its correct location in the above image, just to show its position)
Note that each Hall sensor will switch on and off several times during the full stroke of the slider. This is the result:
We can then place bands across these ‘on’ and ‘off’ positions which represent a unique sequence for L1, L2, L3 & L4
For example, if we say ‘on’ is 1 and ‘off’ is 0 then:
Park = 1,1,0,1
Reverse = 1,1,1,0
Neutral = 1,0,1,1
This logic is what the controller uses to determine the position of the slider, and therefore the gear position selected by the driver. Note that the D position has several bands i.e. 0,0,0,1 and 0,0,1,0 and 0,1,0,0 and 1,0,0,0. Presumably this is because some car manufacturers still use the gear lever to select lower gears manually and these bands represent (say) gears 5, 4 and 3.
Although this technique can be used to confirm if there’s an issue with the gear position switch, fixing it is quite a different problem. First of all, the PCB with the four Hall sensors mounted on it is embedded in potting compound and it looks like it would be an absolute nightmare to dig the circuit board out of the potting compound and resolder the connections, to replace it. I’d be very interested to hear if anyone has tried this, and how successful it was.
Regarding replacing the complete switch assembly (which would include the input speed sensor) I’m not aware of anyone who can supply new switches. I’ve seen plenty for sale for the Continental/Siemens module with the ribbon cable, used in the 6HP28 (see below) but none for the Bosch modules with the spot-welded conducting bars. Clearly, though, used ones are available.
6HP28
There are also an increasing number of posts on the forum regarding the unreliability of the inhibitor/gear position switch for the ZF 6HP28 transmission used in the 5.0 naturally aspirated and supercharged versions of the L322. Although the 6HP28 did include some uprated parts to increase its torque capacity, the main difference between it and the 6HP26 was the Mechatronic unit which had been redesigned to massively speed up the gearshifts. ZF changed manufacturers for the electronic module from Bosch to Continental/Siemens, at least for Range Rovers up to VIN DA765413. From VIN DA765414 they reverted back to Bosch Mechatronic units, although there can’t have been many of these 2013MY vehicles produced. The electronic module design for the Continental unit is quite different to the Bosch one, for which all the connections were made by metal connecting bars joined with spot welds, as the Continental units use a ribbon cable to provide all the electrical connections.
The inhibitor/gear position switch is also different, with a different PCB on which the Hall sensors are mounted. It’s a little more challenging due to access to the connections but my plan is to test a Continental/Siemens switch as well, to see if there are any differences to the Bosch switch.
Phil
