Retrofit D2/Bosch P38 Cruise Control ECU into D1/GEMS P38

ERover82

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Nov 26, 2011
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How to: Retrofit D2/Bosch P38 Cruise Control ECU into D1/GEMS P38

Below is the D1/GEMS P38 cruise control ECU. They're unreliable and fail often.
DSC00067[1].jpg

This is a D2/Bosch P38 cruise control ECU with pigtail. They're cheap, abundant, and more reliable.
DSC00073[1].jpg

Extract the guts.
DSC00069[1].jpg
 
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ERover82

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Re: Retrofit D2/P38 Cruise Control ECU into your D1

Cut off the connector. I used a rotary cut off tool.
DSC00071[1].jpg

Solder the pigtail to the connector using the information below. Then insulate it with liquid electrical tape.
DSC00072[1].jpg

Now you have this:
DSC00075[1].jpg
 

ERover82

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Nov 26, 2011
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Re: Retrofit D2/P38 Cruise Control ECU into your D1

Reinstall. It fits perfectly in the stock location.
DSC00076[1].jpg

Selecting a D2/P38 cruise control ECU:

There are several different tunes for the D2/P38 cruise control ECUs, depending on engine size (4.0 vs 4.6). If you have a 3.9 or 4.0 engine, get an ECU from a 4.0 D2/P38 for smoothest operation. A 4.6 ECU will work, but with less smooth operation.

Make sure it includes the pigtail so you can make an adapter. Our common used LR parts suppliers can do this upon request.


Pinouts:

D2 and Bosch P38 cruise control ECU's use the same pinout but with different pigtail wire colors. Use this pinout information to match you old D1/GEMS P38 ECU's connector pins to the new ECU's pigtail. D1 and GEMS P38 wire colors are the same but pinout is different. The Diagnostic Line wire will be unused in the conversion.

D1 cruise control ECU (AMR 1173):
Pin 1: Orange/Blue - Actuator Pump Power
Pin 2: Not Used
Pin 3: Grey/Yellow - Set Button (from inverter)
Pin 4: Red/Yellow - Resume Button (from inverter)
Pin 5: Green/Purple - Brake Light Switch
Pin 6: Orange/Pink - Actuator Valve Control
Pin 7: Orange/Red - Actuator Pump Control (thicker gauge)
Pin 8: Black - Earth or Ground
Pin 9: Orange/Red - Brake Pedal Vent Switch (thinner gauge)
Pin 10: Orange/White - ECU Power +
Pin 11: Yellow - Speed Signal
There are two wires with the same color-code of Orange/Red but one is thicker than the other as noted above

D2 cruise control ECU (AMR 5700):
Pin 1: Orange/Red - Brake Pedal Vent Switch
Pin 2: Red/Yellow - Resume Button
Pin 3: Not Used
Pin 4: Grey/Yellow - Set Button
Pin 5: Green/Purple - Brake Light Switch
Pin 6: Not Used
Pin 7: Orange/Red - Actuator Pump Control
Pin 8: Orange/White - ECU Power +
Pin 9: Not Used
Pin 10: Not Used
Pin 11: Orange/Blue - Actuator Pump Power
Pin 12: Not Used
Pin 13: Not Used
Pin 14: Not Used
Pin 15: Yellow - Speed Signal
Pin 16: Pink/Red -Diagnostic Line (Unnecessary for conversion to GEMS)
Pin 17: Orange/Pink - Actuator Valve Control
Pin 18: Black - Earth or Ground

D2 cruise control ECU (AMR 5700):
Pin 1: Purple/Green - Brake Pedal Vent Switch
Pin 2: Blue/White - Resume Button
Pin 3: Not Used
Pin 4: Red/White - Set Button
Pin 5: Green/Grey - Brake Light Switch
Pin 6: Not Used
Pin 7: Black/Red - Actuator Pump Control
Pin 8: White/Yellow - ECU Power +
Pin 9: Not Used
Pin 10: Not Used
Pin 11: White/Blue - Actuator Pump Power
Pin 12: Not Used
Pin 13: Not Used
Pin 14: Not Used
Pin 15: Pink/Green - Speed Signal
Pin 16: Pink - Diagnostic Line (Unnecessary for conversion to GEMS)
Pin 17: Black/Yellow - Actuator Valve Control
Pin 18: Black - Earth or Ground

D2 to D1/GEMS P38 Conversion
White/Blue -> Pin 1: Orange/Blue
Red/White -> Pin 3: Grey/Yellow
Blue/White -> Pin 4: Red/Yellow
Green/Grey -> Pin 5: Green/Purple
Blue/Yellow -> Pin 6: Orange/Pink
Black/Red -> Pin 7: Orange/Red (*thicker gauge)
Black -> Pin 8: Black
Purple/Green -> Pin 9: Orange/Red (*thinner gauge)
White/Yellow -> Pin 10: Orange/White
Pink/Green -> Pin 11: Yellow
 
Last edited:

fishEH

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Jan 26, 2009
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Lake Villa, IL
I've done this mod with success as well. Here's some pics/notes.
Cut the solder joints ont the back of the board, preserving as much of the pins as possible.


Then I straightened the pins to have more real estate to solder onto.


Wires soldered on.


Heat shrink


And liguid and regular electrical tape.


Works great!
 

chris snell

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Staff member
Aug 15, 2005
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Those bare solder joints make me a little nervous. When I make cables like this--especially if it's something safety-critical like cruise control--I like to put tiny heat shrink on each wire before soldering them onto the connector. I push them up and out of the way while I'm doing the soldering and then once it's made and continuity checks out, I push them down over the exposed joint and heat them. Then I push a larger piece of heatshrink over the whole bundle.

Nice write-up, though. You guys have set the standard!
 

jymmiejamz

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Dec 5, 2004
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Los Angeles, Ca
Is there a reason you guys aren't just cutting the connector off on the harness side of the D1 and putting the DII connector on the D1 harness?
 

fishEH

Well-known member
Jan 26, 2009
6,927
201
Lake Villa, IL
Those bare solder joints make me a little nervous. When I make cables like this--especially if it's something safety-critical like cruise control--I like to put tiny heat shrink on each wire before soldering them onto the connector. I push them up and out of the way while I'm doing the soldering and then once it's made and continuity checks out, I push them down over the exposed joint and heat them. Then I push a larger piece of heatshrink over the whole bundle.

Nice write-up, though. You guys have set the standard!
Chris, I put a liberal coat of liquid electrical tape over all the solder joints.

Is there a reason you guys aren't just cutting the connector off on the harness side of the D1 and putting the DII connector on the D1 harness?


Jimmie, my main reason is that all the work I did could be done in my heated/cooled workshop in the basement while drinking a beer in my underwear. In other words, I didn't have to contort myself on the passenger floor and cut and splice wires. Its plug and play.
 

p m

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Is there a reason you guys aren't just cutting the connector off on the harness side of the D1 and putting the DII connector on the D1 harness?

I see no reason for it except for what Brett said. Don't remember how far I can pull out the D1 connector to get to the wires with a soldering iron.
 

jymmiejamz

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Dec 5, 2004
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Los Angeles, Ca
Jimmie, my main reason is that all the work I did could be done in my heated/cooled workshop in the basement while drinking a beer in my underwear. In other words, I didn't have to contort myself on the passenger floor and cut and splice wires. Its plug and play.

I can appreciate that. I'm picking up a D1 this weekend, so if it needs it, I'll do this.
 
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p m

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Thank you Eric,

now, for the first time in about 15 years, I have a working cruise control in my 260-kmi D1!

Of course, not a single thing stated about Land Rovers is a "fact;" wire colors were completely different on both D1 and D2 side. It's an early GEMS D1 - maybe GEMS trucks are closer to Bosch trucks than earlier ones. In any case:

- using the pin/circuit list from this thread was critical, more so than the wire color. I'll throw in a $0.0002 table with pin-to-pin cross-list and wire colors on my truck (and on that AMR5700 pigtail). FWIW, I found it easier to cut off and resolder wires than unsolder or cut off a header from AMR1173 to make an adapter.

EDIT: As it turns out, you can have somewhat-working cruise control - I've been wondering for some time why would it not keep the speed above 70 mph. The reason was the pump - working, but barely; I noticed that the throttle was never open more than 40% with the original pump. Replaced with a different pump - pulls nice and strong now.
 

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