Intermittently will not start

RIC B

MEMBER
2007 MERCURY MARINER
6 CYL
4WD
AUTOMATIC
140,000 MILES

My vehicle has an issue that very sporadically it just does not start. It may go for months without a problem, but then does not start. The dash lights do not work when this occurs but all other power seems to work. In the past, I have been able to pull out the far left module under the hood right under the windshield. There are 3 of them and I disconnect the one closest to the passenger side. I have left it unplugged for a few hours, came back and plug it back in and then it started right up. I have replaced the battery, had the keys reprogrammed, replaced the key cylinder and verified the starter and alternator are okay. Any other suggestions?

Thursday, September 9th, 2021 AT 1:46 PM

3 Replies

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi,

When this happens, does the starter fail to engage? Also, can you take a pic and upload it of the module you are referring to. I've gone through the engine wiring schematic for the powertrain management circuits, transmission circuits, and so on and everything indicates the module to be in the center of the firewall.

Since you get it to work by disconnecting and reconnecting the module, have you checked to make sure there isn't a pushed-in pin, corrosion, or a damaged connector pin in the connector?

Let me know. Also, here is a link that explains how to check wiring and connectors. Take a look through it and let me know if it helps.

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

Let me know.

Joe

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Thursday, September 9th, 2021 AT 6:25 PM

RIC B

MEMBER
2 POSTS

Thanks for the reply. When I turn the key, I can hear a slight click but that is all. None of the dashboard lights come on except the words “Mercury Mariner”. I did clean out the connector and did not notice any damage to pins or corrosion.

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Friday, September 10th, 2021 AT 7:58 AM

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi,

Okay, that is the PCM. It has three connectors going to it. The idea that you lose the dash lights is making me think it is a ground issue.

I attached a portion of the powertrain control circuit below. II highlighted ground wires that come from the PCM. Here is what I need you to do:

Locate the black ground wires from the PCM. It will be on the firewall. Check the connection for corrosion, a loose connection, or damage to the wiring.

Next, note in the schematic where it indicates S104. That indicates a splice in the wiring, Several wires are joined together. It isn't uncommon for a splice to corrode and lose connection. Check that also.

Let me know what you find.

Joe

See pics below. Note: the schematic was one page long. I cut it in half to make it readable for you. I did overlap them so you can follow from one to the next.

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