Code P0642 sensor reference voltage a circuit low

LENNIE PATTON

MEMBER
2006 MERCURY MOUNTAINEER
4.6L
V8
4WD
AUTOMATIC
160,000 MILES

I'm getting this generic code P0642 with four flashing red lights indicating a failure in one or more of the following areas: (the red lights) (1) evap sensor monitor (2) oxygen sensor monitor (3)oxygen sensor heater monitor (4)catalysts sensor monitor. This has been a nightmare trying to figure out what is going on. I've replaced the cam and crank sensors, fuel pressure sensor and now it won't even start.

10 Replies

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello,

Could you please double check the Direct Trouble Code (DTC) number again. I show no listing for DTC P0642.

Thanks,
Alex
2CarPros

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Tuesday, March 19th, 2019 AT 3:27 PM

LENNIE PATTON

MEMBER
6 POSTS

It's a generic code. Sensor reference voltage A circuit low. The red lights indicate a malfunction of some sort.

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Saturday, March 23rd, 2019 AT 3:03 PM

LENNIE PATTON

MEMBER
6 POSTS

There was no answer only a question that I answered and never got a reply.

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Sunday, March 24th, 2019 AT 10:32 AM

KEN L

MASTER CERTIFIED MECHANIC
48,289 POSTS

Sorry I am not sure what you are saying?

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Monday, March 25th, 2019 AT 10:32 AM

LENNIE PATTON

MEMBER
6 POSTS

I gave the code P0642 and was told to check it again because they couldn't find a p0462 code. I explained it's a generic code saying "reference circuit low" then gave information that I had my alternator checked and it checked good. I never got any answer back.

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Tuesday, March 26th, 2019 AT 8:32 AM

LENNIE PATTON

MEMBER
6 POSTS

I even sent a picture of the Ob2 scanner with the code pulled up on the screen.

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Tuesday, March 26th, 2019 AT 8:33 AM

KEN L

MASTER CERTIFIED MECHANIC
48,289 POSTS

Sorry about that. I thought you were saying the alternator was bad and they missed it. anyway lets check fuse number 24 on the left side of the drivers compartment for power. If okay lets test the wiring between the alternator and PCM/cluster and if okay the PCM or cluster is bad and needs to be replaced. here is a guide to help us get started and the alternator wiring diagrams and fuse locations so you can do the test to confirm the issue:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

and

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

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