Epson ET-8550 Scanner Error Codes 100017 and 100016: What They Mean and How to Fix Them

Question

After following guidance to fix scanner code 100017, I'm now getting scanner code 100016 on my Epson ET-8550. I'm trying to figure out how to tighten the scanner belt and get it running correctly. 

Answer

You already made an important observation: you resolved scanner code 100017, but then scanner code 100016 appeared. That usually means you fixed one failure point in the scanner system, and now the printer is able to proceed far enough to detect the next failure point.

What scanner codes 100017 and 100016 usually indicate

On the ET-8550, the scanner assembly relies on three things to "boot" correctly:

1. Scanner carriage movement (belt, rails, and mechanical drag)

2. Scanner motor drive (motor strength, gear engagement, encoder feedback)

3. Scanner communication (FFC cables and connector seating)

When something is off, the printer throws scanner startup/stall errors. In practice:

• 100017 commonly shows up when the scanner can't initialize due to communication problems (a scanner FFC not seated, damaged traces, wrong routing, or intermittent connector contact) or a mechanical stall so early that initialization fails.

• 100016 commonly shows up when the scanner is detected and starts to move, but then it stalls, misreads position, or can't reach expected timing/position. This points more strongly toward motor/drive/belt drag, but it can still be caused by an intermittent FFC because communication dropouts can look like "position lost."

That's why your instinct about the belt makes sense-but I want you to check the scanner motor and the scanner FFC cable first, because "belt tightening" is less adjustable on these units than people expect, and overtightening can create new problems.

Step 1: Inspect the scanner motor (most likely for 100016)

Your next step should be to check the scanner motor and its drive path:

Signs the scanner motor/drive is the issue

• Scanner starts moving, then stops and errors (100016)

• Grinding, chirping, or a "stuck" sound

• Movement is jerky instead of smooth

• Works once after power reset, then fails again (weak motor or binding)

What to do

• Power off and unplug the printer.

• Open the scanner area (top assembly access) and gently move the scanner carriage by hand (if accessible).

  • It should move smoothly with consistent resistance.

  • If it binds at a certain spot, look for: pinched wiring, belt rubbing, foreign debris, or a rail that's dry/dirty.

• Check the motor gear (if visible) for cracked teeth or slipping.

• If the motor spins but the carriage doesn't move correctly, the issue may be gear engagement or a belt that's skipping due to contamination or misalignment.

Important: A scanner can throw 100016 if the motor is fine but the carriage is dragging. The system expects the scanner to reach a position within a set time; if it can't, it errors.

Step 2: Check the scanner FFC cable (very common after a repair)

Since you just worked through 100017, the FFC cable is still a prime suspect. Even when it "looks seated," it can be off by a hair.

What commonly goes wrong with scanner FFC cables

• Cable not fully inserted into the ZIF connector

• ZIF latch not locked evenly

• Cable inserted at a slight angle

• Cable crease causing hairline trace breaks

• Cable routed so it flexes sharply and fails intermittently

• Contact contamination (finger oils, residue)

What to do

• Reseat the scanner FFC cable on both ends (scanner side and mainboard/control side, depending on routing).

• Inspect the gold contacts:

  • If they're dull/dirty, gently clean with high-percentage isopropyl alcohol and let dry fully.

• Inspect the cable for:

  • White stress lines, sharp folds, or kinks

  • Any exposed copper or damaged insulation

• Make sure the cable routing matches the factory path:

  • If it's routed too tight, it can tug during movement and cause intermittent disconnects-this can trigger 100016 after you solved 100017.

If your fix for 100017 involved replacing or reseating a cable, it's very possible the system is now "working enough" to move-until the carriage hits a point where the cable flexes, and then it loses signal and throws 100016.

Step 3: About "tightening the scanner belt" on the ET-8550

On many Epson scanner mechanisms, the belt tension is not meant to be "tuned" like an adjustable timing belt. Tension is typically controlled by the design (spring/idler placement). Still, you can check belt condition and alignment.

What you can do safely

• Confirm the belt is:

  • Not twisted

  • Not riding up on a pulley edge

  • Not rubbing a frame surface

• Check pulley alignment:

  • A pulley that's slightly out of line can cause belt walk and stall

• Look for belt contamination:

  • Grease/oil on the belt can cause slipping (which looks like a position error)

What to avoid

• Don't "over-tension" by forcing the motor mount or pulley position unless you're 100% sure the design supports it. Over-tensioning:

  • Adds drag

  • Overloads the motor

  • Can create a new 100016 stall condition

In other words: 100016 is often caused by drag, so making the belt tighter can make it worse, not better.

Step 4: Quick isolation checks (saves time)

If you want a fast way to narrow it down:

• If the scanner carriage binds by hand → mechanical drag/rail/belt alignment issue (very likely)

• If it moves smoothly by hand but fails consistently under power → motor strength/gear slip, or position feedback issue

• If it fails only at a certain point in travel → FFC routing/flex point problem is very likely

• If reseating the FFC temporarily "fixes it" → cable or connector seating issue (replace cable if damage is suspected)

Addressing printer issues can get complicated because so much of it is hands-on and depends on what you see and feel during disassembly. Because of that, we're not able to provide remote troubleshooting, suggestions, or support for printer repairs. We do offer an in-person evaluation and repair service through our local diagnostic facility: printer repair service (https://bchtechnologies.com/printer-repair-service). Due to high demand, we operate on a first-come, first-served basis, and it may take a few weeks before we can accept a drop-off. Our services are structured to repair either a whole printer or specific parts, with clear instructions on how to proceed. That said, we understand our rates aren't the most economical, so we strongly recommend self-help through online research. A good place to start is YouTube, especially our channel homepage: BCH Technologies on YouTube (https://youtube.com/@bchtechnologies). Use the search icon next to "About" on the right side of the menu bar to find topics quickly. I receive many questions every day asking whether we have a video for a specific issue, and after producing content for years, it's hard to remember every single upload-so YouTube search is the fastest method. It can also suggest other relevant videos from other creators that may help.

Thanks again for reaching out and for supporting BCH Technologies. I really appreciate you taking the time to share your results and error codes (100017 and 100016)-those details help a lot and also help us improve what we cover in future guides.