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Code 51a6?

Tiny
BHAMDOC1973
  • MEMBER
  • 2009 BMW 550I
  • V8
  • 2WD
  • AUTOMATIC
  • 119,000 MILES
Seems like it is in one gear only. Sometimes shifts off while running and harder to start 2nd time.
Tuesday, January 10th, 2023 AT 4:35 PM

23 Replies

Tiny
BORIS K
  • MECHANIC
  • 799 POSTS
Hello,

Code 51A6 is a transmission control module-engine control module communication issue.
Usually, a bad or missing signal from the engine control module.
This can be caused by a bad crankshaft position sensor or damaged/corroded wiring.

The sensor is located on the bottom right of the transmission housing, see image below.
Suggest inspecting the wiring and connector to the sensor first.

Cheers, Boris
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Wednesday, January 11th, 2023 AT 1:53 AM
Tiny
BHAMDOC1973
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  • 1,656 POSTS
Changed CPS, but it is showing these codes.
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Monday, January 16th, 2023 AT 1:35 PM
Tiny
BHAMDOC1973
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  • 1,656 POSTS
More.
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Monday, January 16th, 2023 AT 1:38 PM
Tiny
BORIS K
  • MECHANIC
  • 799 POSTS
Hello,

Looking at the fault codes you still report a crankshaft sensor fault.
Are you sure that you replaced the correct sensor at the transmission housing?
You report replacing the CPS sensor, which is a camshaft position sensor.
See image below for the location of the CKP sensor.

The intelligent battery sensor is located at the negative terminal of the battery.
This sensor can also cause no start no crank issues.

See good video:
https://youtu.be/vl7BkzQBgHY

Cheers, Boris
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Tuesday, January 17th, 2023 AT 2:13 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
Yes, I replaced the crank one by the transmission housing. Not OEM. Let me check the intelligent sensor.
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Tuesday, January 17th, 2023 AT 5:12 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
Also, there is an aftermarket filter that is not installed properly, but the MAF is still in place, I would think regardless of connecting this tube it should run okay.
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Tuesday, January 17th, 2023 AT 7:00 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
There is also some water on driver side floor that I noticed, is it possible something on the inside is shorting and causing this mess backward?
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Tuesday, January 17th, 2023 AT 7:08 AM
Tiny
BORIS K
  • MECHANIC
  • 799 POSTS
Hello,

This contraption of intake system should not cause starting or idling issues but keep in mind that this will cause contamination of the MAF sensor and the obvious dirt ingress into the engine.

I would certainly strip the carpet back and check any surrounding wiring, connectors and modules for possible corrosion.

Cheers, Boris
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Tuesday, January 17th, 2023 AT 7:15 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
Cleaned out MAF and it started much better, RPM steady.
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Tuesday, January 17th, 2023 AT 7:22 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
Still some codes, with the scan er still shows in limp mode Nd 3rd gear.
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Tuesday, January 17th, 2023 AT 9:24 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
Can you check if this car has a fuse for the crank shaft position sensor? Also, I read some forums stating that their issue was solved after replacing the thermostat.
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Tuesday, January 17th, 2023 AT 9:35 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
I checked wires on the crank sensor using a probe, one is ground, one battery voltage and the other just reads 10.3, does not say volts, does not beep or light up. I don't know if this is an issue.
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Wednesday, January 18th, 2023 AT 8:27 AM
Tiny
BORIS K
  • MECHANIC
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Hello,

The crankshaft position sensor is supplied with 12V on orange wire from fuse F005(30A), see image 2 below.
The black/white wire is ground.
The yellow/white wire is the signal wire back to the DME pin 27, see image 3 below.
When the crankshaft sensor is disconnected then the DME will send a reverence voltage back up the signal wire.

How to test the sensor:
https://youtu.be/AacxF8dv_Sw

Cheers, Boris
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Friday, January 20th, 2023 AT 9:21 AM
Tiny
BHAMDOC1973
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  • 1,656 POSTS
What is a reverence you mean reference? But I have is 10.3 and does not say volts.
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Friday, January 20th, 2023 AT 9:34 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
I also looked at where the ivm is which also contains the ECM, but could not see any fuses.
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Friday, January 20th, 2023 AT 9:36 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
But since am getting 12v and ground it should be okay.
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Friday, January 20th, 2023 AT 9:36 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,656 POSTS
A new genuine crank shaft sensor has taken care of the code and it does not stall. Now I have to find a vacuum leak because there is a bit of rpm up/down when you first start it. I only drive it around my driveway and 1st and 2nd shifted so it's out of limp mode but did not shift 3rd not sure why yet.
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Saturday, January 21st, 2023 AT 2:49 PM
Tiny
BORIS K
  • MECHANIC
  • 799 POSTS
Hello,

The best way of finding a vacuum leak is by using a smoke tester. A lot of people like spraying brake cleaner or carburetor cleaner to try find a leak but this can be hazardous as these liquids are flammable.
See image below regarding a smoke tester .

How to use a smoke tester:
https://youtu.be/LV2Cx41IccU

Cheers, Boris
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Monday, January 23rd, 2023 AT 3:37 AM
Tiny
BHAMDOC1973
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  • 1,656 POSTS
Does the intelligent sensor have a fuse?
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Monday, January 23rd, 2023 AT 1:51 PM
Tiny
BORIS K
  • MECHANIC
  • 799 POSTS
Hello,

I have searched a lot of documentation but cannot seem to find a fuse for the power supply for the IBS, intelligent battery sensor.

See image below for the sensor layout.

Cheers, Boris
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Tuesday, January 24th, 2023 AT 9:34 AM

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