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Jake, Nissan Technician
Category: Nissan
Satisfied Customers: 3931
Experience:  Experienced collision repair technician, Pulaski Tech graduate and DSM hobbyist.
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Ok I have a 2004 Nissan Maxima with p1229 p2138 code I am

Customer Question

Ok I have a 2004 Nissan Maxima with p1229 p2138 code I am checking the terminal 90 and 91 at the computer and I have 5vlt on 91 but at terminal 90 I have 3.5 volts with the switch on but,it drops to 2.3 after couple minutes .. So I'm trying to find out what are the other sensor that share my 5volts reference because what I see on my Michell diagram is that terminal 90 goes direct to my app sensor I don't see nothing else that share that 5volts reference . Can you pin point it to me if I'm missing something that shares that 5 volts reference . Because the p1229 says sensor power supply short
Submitted: 1 year ago.
Category: Nissan
Expert:  Clayso replied 1 year ago.

Hi There, I'm Clayso a certified master automobile technician with 30 years of automotive repair and diagnostic experience.

The DTC P1229 is for a shorted 5 volt reference circuit. The 5v reference can be pulled down by the TPS, APS, MAF, power steering pressure sensor, refrigerant pressure sensor, and the EVAP pressure sensor. Disconnect these one at a time and see when the 5v reference returns. Visually check the wiring around these component connectors.The Red wire is the 5 volt reference to these sensors. Terminal 90 at the ECM does go directly to a potentiometer in the APS sensor that connects directly back to the ECM. I've seen A/C and EVAP pressure sensors cause the same problems.

I hope this information is helpful. If you have any questions let me know. You can reply back to me through this thread at any time.

Kindly rate my assistance in a positive manner so I may have credit for helping you.
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Customer: replied 1 year ago.
Can I get a diagram for all this please
Expert:  Clayso replied 1 year ago.

The transfer of information between the TPS, APS, MAF, power steering pressure, refrigerant pressure, and the EVAP pressure sensors all takes place within the ECM. As I said earlier disconnecting each of these components one at a time until the 5v reference returns will reviel any sensor shouted and pulling down the reference.

I have complete diagrams for all of these systems from several different sources and/or I can make a complete powertrain system diagram. I can offer a premium service for 5 bucks and continue this conversation through regular email and or the phone, which ever works best. I can provide diagrams and technical information specific to this problem for this vehicle. Regular email is so much easier for sending technical information, diagrams and images. It's also straightforward for you to send me images from your phone. Please accept my offer for 2004 Maxima P1229 & P2138 so I can better assist you.

Let me know


Customer: replied 1 year ago.
I found the problem but now why my rpm and engine temp and mpg don't work
Expert:  Clayso replied 1 year ago.

What did you find and what did you do?

Let me know


Customer: replied 1 year ago.
My power steering pressure sensor was short out
Customer: replied 1 year ago.
But my battery went dead and after a charged it now my cluster don't. Work
Customer: replied 1 year ago.
My fuel level my temp and my tach won't work
Expert:  Jake replied 1 year ago.

Hey there, new expert here.

The problems your experiencing now are likely a result of the a/c auto amp. Do you ever put change on the shelf in front of the center display?

Customer: replied 1 year ago.
What's the ac auto amp what's the location do I need to replace it and if I do replace it does it need to be reprogram
Expert:  Jake replied 1 year ago.

The a/c auto amp controls the combination meter and hvac controls

Customer: replied 1 year ago.
Is that the white box under the stereo or where is it
Customer: replied 1 year ago.
Do I need to reprogram if I replace it
Expert:  Jake replied 1 year ago.

You need to replace it, if it has a coin in it as it shorts out some of the circuits by bridging and grounding them.