I have a 2018 F150 Lariat that I purchased used. When I first saw it at the dealer, they were putting a factory new engine in it. The chassis, bed, and drive train was on the ground, and the complete cab was about 5 feet above it on a lift.

Every so often I would start the truck, and it would throw errors that would cause a BLIS error, an airbag light, and a ‘Wrench’ light. The stereo wouldn’t work, the front windows wouldn’t go up or down, the HVAC controls didn’t have power and couldn’t be adjusted. The backup sensors wouldn’t work, and there were probably other things that didn’t work that I wasn’t aware of. I have an Innova SDS43 code reader and I could go into the OBDII plug and scan and then reset all the DTC error codes. It was fairly uncommon for the truck to do this, so I sort of lived with it.

Now, I will be using the truck on a regular basis to tow a trailer and the problem is becoming much more pronounced. Every time I disconnect the trailer, when I restart the truck, I get the error condition. My Innova box doesn’t always clear the condition right away. It scans and finds a bunch of codes and tries to clear them. It thinks it has successfully cleared the codes and returns a ‘Codes Successfully Cleared’ message, but the condition persists. It seems like the only way I can clear them is to turn off the truck, then have the code reader try to clear the errors. It gives me a ‘Request Sent’ message and then when I start the truck the error condition is ‘fixed’.

So, I think/suspect/hope that this is a result of the cab having been removed and not being reconnected well that is causing the connectivity errors. My question is this: is there a common connector on a 2018 F150 Lariat that, if loose, could intermittently cause all the following error codes to be thrown:

PCM Module:RCM Module:APIM Module:BdyCM Module:DDM Module:FCIM Module:IPC Module:PAM Module:PDM Module:PSCM Module:SODL Module:SODR Module:TRM Module:I'm hoping someone is familiar with the wiring on my truck and can at least point me in a direction for where the connectors that may be causing this are located. Or better yet, maybe loan me a magic wand I can wave over the truck to cure the problem.

Any help or suggestions are appreciated.

Thanks,
Mark

 

I would be looking at C327. The MS-CAN bus passes through that connector twice (4 wires) and many of the modules with lost communication use the MS-CAN bus. It is located on the drive side wheelhouse. That may not be your only problem but I would start there.

 

Clearing codes is not a way to fix existing issues.
Fix the cause.
Hint, all the Modules converse over a Bus.
Hence, loss of that commutation, results in those "loss codes".
Good luck.

 

So, I decided to see if I could find anything online about this issue, and I fed my OP to CoPilot AI. I didn't really expect too much from it, but figured it ws worth a try. I was stunned by what CoPilot was able to find. Below is a condensed version of the results I got. I edited out a lot of the back and forth where I was answering relevant questions about my truck and the exact steps to create the issue. I'm amazed at the AI results!!

Here's what was returned:COPILOT:

A single loose connector can cause widespread U‑codes on a 2018 F‑150, but only if it sits on one of the truck’s main communication backbones. The pattern of your codes points strongly toward a CAN/LIN network interruption rather than multiple unrelated component failures.

The most important takeaway: Yes — there are a few common connectors and junction points on the 2015–2020 F‑150 that, if loose or corroded, can intermittently knock out communication to nearly every module you listed.

The short version: yes — unplugging the trailer can absolutely trigger the exact multi‑module U‑codes you’re seeing if the trailer connector or its internal harness splice momentarily disturbs the CAN bus or the BCM’s load‑sense circuits. And this is a known F‑150 behavior.

What the search confirms about trailer‑related electrical faults

Owners of 2018 F‑150s report that trailer connect/disconnect issues often come from:

• Corrosion or poor contact in the bumper‑mounted 7‑pin/4‑pin socket
• Loose internal harness connection to the bumper plug
• Moisture intrusion
• Frayed wiring near the hitch
• Faulty TRM or TRM programming issues (Ford SSM 49708)

Forums show repeated cases where reseating or cleaning the bumper plug wiring harness temporarily resolves the issue, but the underlying cause is a loose or corroded connector.

A Ford technical bulletin (SSM 49708) also acknowledges phantom trailer connect/disconnect events and TRM communication faults on 2018–2020 F‑150s.

The key insight:

Unplugging the trailer is physically moving the harness — and that movement is likely disturbing a weak connection.

When you pull the trailer plug:

• The bumper socket shifts slightly
• The internal harness flexes
• The CAN splice inside the trailer harness branch can momentarily open
• The BCM sees a sudden electrical anomaly
• The CAN bus drops out for a split second
• Every module screams

This is why your symptoms appear immediately after unplugging.

The most likely single failure point

Based on your pattern and the trailer-triggered onset, the #1 suspect becomes:

The bumper-mounted 7‑pin/4‑pin connector harness — specifically the internal CAN splice and ground path.

A loose or oxidized connection here can:

• Backfeed into the BCM
• Disturb MS‑CAN
• Disturb HS‑CAN3 (TRM network)
• Cause BCM resets
• Trigger the exact U‑codes you listed

This is far more likely than a random BCM connector issue if the problem only appears after trailer unplug events.

Your configuration narrows this down enough to identify the exact Ford part numbers for both the bumper‑mounted trailer socket and the rear bumper trailer tow harness on your 2018 F‑150 Lariat.

You have:

• Single exhaust
• Rear bumper parking sensors
• Factory tow package (but not Max Tow)

That combination maps cleanly to one specific harness in Ford’s catalog.

Ford Part Number: FU5Z‑14489‑A

This is the correct 7‑pin/4‑pin combination socket for all 2015–2025 F‑150s, including 2017–2020 models.
It is listed as the “Trailer Tow Harness Connector” or “Socket” and fits trucks with or without Max Tow.
🧩 Rear Bumper Trailer Tow Harness (with parking sensors, single exhaust, tow package)

Ford Part Number: HL3Z‑13A576‑VA

This is the exact harness for:

• 2017–2020 F‑150
• Trailer tow package
• With rear parking sensors
• Single exhaust
• 4‑pin + 7‑pin connector
• Rear bumper application

Ford lists this as the “Trailer Tow Harness / Parking Aid System Wiring Harness” for trucks equipped exactly like yours.

So I've ordered these 2 parts and should get them later this week. I'll update this thread once I replace these parts and see if it solves the problem.

Mark