Two “key” error codes.

P0850 and B2604

 

Backstory? Issues? Symptoms? Does you car have the ESCL module? Was it disconnected? Being that both the iKey AND the IVIS warning lights are on indicate something serious is going on with that car. BCM?

Dealer can't diagnose? Did they say why? Being there is a open recall campaign on the 2013-2015 Nissan Rogue/ Altima/ Pathfinder for the same B2604 code they should know a little something. In the recall, Nissan has to readjust the shift rod (console to gearbox) to solve that problem.

As for the P0850, that could the PNP range switch located in center console/ shifter (these are known to get dirty) or the "sensor" located in the TCM.

Again, the more you can provide upfront will give us more clairty when proffering solutions.

 

Infiniti ran complete diagnosis. No idea what problem was. Didn’t charge me. Replaced shifter assembly and still have error codes plus “

check engine” light. Car shifts and starts fine. I just hope they are no further problems.

 

Is that printout from the Infiniti dealership?

Then more than likely the issue lies in the TCM. Nothing you can do about it short of replacing the transmission or the TCM as the PNP sensor is not user-serviceable on the 7AT.

Maybe others will have other ideas/ thoughts, but if the center shifter didn't resolve the P0850 and assuming the shift rod is properly adjusted (B2604) then it has be a internal fault within the TCM. Harness issue, while possible, is exceedingly rare for these codes.

 

Yes. That is the printout from the Infiniti dealer in Thousand Oaks CA.

 

Part you need (most likely)



Park / Neutral Position Switch (aka Range Switch)

• OEM Infiniti / Nissan part number:

31918-1XF0A

• Fits: 2009 G37x AWD (RE5R05A 7-speed)

• Cost:

• OEM: ~$120–$180

• Aftermarket: cheaper, but OEM is safer here



You can try adjustment first, but given your “only in D/R” symptom, replacement usually ends it permanently.



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Where it is

• Driver side of the transmission

• Outside the transmission (no pan removal)

• Bolted where the shift linkage connects



Replacement overview (no BS)



Time: ~45–60 minutes

Tools: 10mm & 12mm sockets, ratchet, marker



Steps

1. Disconnect battery (important)

2. Put shifter in Neutral

3. Mark current switch position (paint pen)

4. Unplug electrical connector

5. Remove shift cable from lever

6. Unbolt old switch

7. Install new switch loosely

8. Align to Neutral (critical step)

9. Tighten bolts

10. Reconnect battery

11. Clear codes

12. Test D / R



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Alignment (this matters)

• Switch has alignment marks

• Transmission must be in Neutral

• If misaligned by even a few mm → same codes come back



This is why shops mess it up.



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Why I recommend replacement over adjustment

• Your switch is working intermittently

• Adjustment helps when it’s just off

• D/R-only errors = internal contact wear

• Adjustment may buy time, replacement fixes it.

 

Normally I would agree that cleaning/ adjusting/ replacing the PNP switch may resolve the issue,. However, OP already replaced the shifter assembly. The odds of both shifters producing the same codes is highly unlikely. Which is why I pointed to the shifter rod being out of adjustment or a internal issue with the TCM.

Still, it is up to OP to decide what path to take.

 

Thanks for your input.

 

Call Justin at Nexenzo in El Monte, CA as he knows the TCM and related error codes well and can sell you a rebuilt valve body and TCM (they are a unit) then also reprogram for you as well (~$650, but he will also give you a few bucks for your core).

https://www.nexenzo.com/collections/all

Since you are in Northern LA, ask if he can also install and tell him someone from the G37 community referred you (this will help differentiate you from others that call and waste his time).

He's a good guy, just busy and its days before Xmas, so be patient.