The reorder was supposed to be identical, but the parts had changed
Managing engineering changes (ECN) at Chinese factories - what factories change without telling you, how buyer-requested changes go wrong, approved samples, BOMs and change request forms, contract clauses, how to catch hidden changes, and a checklist

Hello, this is GreenFrog Seoul.

A company importing small humidifiers sold its first order of 3,000 units without trouble, then reordered 5,000 units from the same factory. About a month after the second batch arrived, reviews saying "it got louder" and "it leaks" started piling up. When the team took apart a unit from each batch side by side, the internal pump came from a different manufacturer, the component layout on the circuit board had changed, and the water tank wall was 0.3 mm thinner.

When they confronted the factory, the answer was: "Performance is exactly the same. We only changed the parts supplier." Performance was not the only problem, though. The Korean KC certification had been tested on the first batch's board and component set, so strictly speaking the changed product was not the product that had been certified. The importer had to stop sales and figure out what to do with the remaining stock.

Factories changing specifications without telling the buyer is very common in China sourcing. Changes the buyer requests can also cause trouble when they are not managed properly. The process for controlling these changes is called engineering change management, built around the ECN (Engineering Change Notice). This post covers what factories commonly change, how a change approval process works, the clauses to put in your contract, and how to catch changes made behind your back.

To a factory, switching a parts supplier is often just a "小改动" (a small change). Saving a few percent on cost is a big win for the factory, and if the buyer never notices, nothing happened. Unless the duty to notify you of changes is written down, the factory has no reason to tell you.

1. What engineering change management is

Engineering change management is the process that defines, whenever an approved product specification changes, who requests the change, who reviews its impact, who approves it and when it takes effect. Manufacturers usually split it into the change request (ECR, Engineering Change Request) and the change notice (ECN, Engineering Change Notice). Chinese factories call it "工程变更通知" or simply "变更通知".

Factories that supply large companies are used to this process, but factories that mainly do small-volume OEM often keep no change history at all. When you work with factories like that, it is more realistic for the buyer to set the forms and require them.

2. What factories most often change without telling you

Most of the changes we actually see in our consultations start with cost cutting or material supply problems.

We covered color and material drifting from lot to lot in Episode 45, and factories secretly subcontracting in Episode 115.

3. Changes the buyer requests go wrong too

Engineering changes do not only come from the factory side. After the first sales, it is natural to reshape a handle based on customer feedback, move a logo or add a color. The trouble starts when these requests are exchanged as quick chat messages.

You send "gray buttons from the next order" on WeChat, and the factory applies it to the batch already in production, so one container arrives with two colors mixed together. A mold gets modified, but pre-change parts are still in the warehouse and end up mixed in. Many disputes also arise later because nobody agreed who pays for the mold modification and the leftover materials. For mold ownership and modification costs, see Episode 109.

4. The basic tools of change management

You do not need a complicated system. These four tools are enough to prevent most problems.

A versioned spec sheet and BOM

Give your spec sheet and bill of materials (BOM) a version number and date, and list the manufacturer and model for every part. Write "Motor, XX Co. RS-385, 12V" rather than "1 motor" so you can tell when the supplier changes. We covered how to write spec sheets and BOMs in Episode 59.

Approved sample (golden sample)

Attach a label with signatures and a date to the sample that defines mass production, and have the buyer and the factory each keep one. When a change is approved, make a new approved sample and mark the old one "void" to avoid confusion.

A change request form

If whoever wants a change has to fill in the fields below and submit them, it becomes hard for a factory to say "we told you verbally."

A change log

Keep every approved change in one table, in date order. If a claim comes up, this table is your evidence of what changed and from when.

5. Clauses for your contract and quality agreement

If you want the factory to notify you of changes, your documents must say the factory is liable when it does not. Put clauses like these into your OEM contract or quality agreement.

• Any change to the approved specification, parts, suppliers or production site must be notified in writing at least 30 days before it takes effect and requires the buyer's written approval
• If an unapproved change is found, the factory bears the cost of returns, rework and certification retesting for the affected goods
• Mold modification costs and leftover material costs for buyer-requested changes are agreed in writing before the change
• Even unavoidable changes, such as a discontinued part, require a sample and specification of the replacement part to be submitted first

For quality agreements in general, see Episode 103.

6. The change approval process step by step

The last step is the one most often skipped. If you approve a change but never check the first production lot, you may find that only the sample changed while production stayed the same, or that parts you never approved changed along with it.

7. How to catch changes made behind your back

Contract clauses are useless if nobody checks. When a reorder arrives, compare it directly with the previous batch.

The easiest check is weighing. When thickness or material changes, weight changes first, so compare the weight of the finished product and its main parts with the approved sample. Take a few randomly selected units apart and compare the part makers' markings, the board layout and even the number of screws against the approved sample. Also check that the manufacturer and model printed on motor, battery and adapter labels match the BOM.

Simple tests give you a first read on materials. A magnet or a handheld analyzer works for stainless steel, and density or smell can flag problems with plastics.

Adding these items to your pre-shipment inspection checklist costs little extra. We covered inspection procedures in Episode 47 and Episode 100.

8. Sample wording to send to the factory

Factories accept change management rules when you set them with the first order. If you bring them up only after a problem, the factory is likely to say "you never mentioned this before." We recommend sending the wording in Chinese as well.

Sample wording (duty to notify)
If you need to change the approved specification, BOM, parts suppliers or production site, please notify us in writing 30 days before the change takes effect and apply it only after receiving our written approval. We will not accept products changed without approval.

Sample wording (reorder check)
Please produce this reorder exactly to spec sheet version 2.1 and the sample approved in March 2026. Before production starts, please send photos of the labels on the main parts (motor, PCB, battery).

Sample wording (buyer-requested change)
Please apply the button color change starting from PO 2026-018. Produce all earlier orders in the existing color, and send photos of the first units produced after the change. Please first tell us the quantity of remaining parts in the old color and the cost of disposing of them.

9. Three real cases

These are anonymized versions of patterns we often see in consultations. Amounts and timeframes are illustrative.

Case 1 — A different pump and board

This is the humidifier importer from the start of this post. When the factory switched pump suppliers, it also modified the board to suit the new pump. The importer stopped sales and recertified the product for KC with the new specification, losing almost two months of sales in the meantime. After that, it added a prior approval clause to its contract and included a teardown comparison in the inspection for every reorder.

Case 2 — Stainless 304 became 201

This importer brought in stainless steel tumblers. In the third batch, returns came in because some inner liners were rusting, and a composition analysis showed 201-series material. The factory said "the material supplier sent the wrong grade," but the purchase order only stated the material grade and did not require a material certificate. The importer now gets a material certificate and magnet test photos for every lot. For importing food-contact products, see Episode 64.

Case 3 — A color change requested by chat

A camping chair importer asked on WeChat for "khaki frames from now on," and the factory immediately applied it to half of the batch already in production. One container arrived with black and khaki mixed together, and returns followed from customers who received a different color from the one on the product page. The importer now requests every change only in a document that states the effective point by PO number. One page stating when the change applies, instead of a one-line message, would have prevented this.

10. Common mistakes

• Assuming the reorder would be identical because the first batch was fine
• Leaving part manufacturers and models out of the BOM
• Leaving the approved sample only at the factory, with none kept by the buyer
• Requesting changes only by chat without setting an effective point
• Approving a change without checking whether it affects certification
• Not checking the first production lot after approving a change
• Not agreeing in advance on mold modification and leftover material costs

11. Engineering change management checklist

First order

• Version numbers on the spec sheet and BOM, with part manufacturers and models listed
• Signed approved samples kept by both the buyer and the factory
• A prior written approval clause in the contract or quality agreement

Change requests

• Description, reason, impact and effective point received on the change request form
• Checked whether certification, price or lead time will change
• Agreed how existing stock and leftover materials will be handled
• New approved sample made and the old one marked void

Reorders and inspection

• Photos of main part labels received before production
• Weight comparison and teardown comparison added to the inspection
• Change log kept up to date

Final thoughts - check "the same product" in writing

Factories usually change specifications because of cost and material supply. That may be a rational choice for the factory, but the returns and certification problems land squarely on the buyer. Rather than relying on the factory's good faith, it is more reliable to build a structure in which changes have to be reported.

You do not need much: a versioned spec sheet and BOM, signed approved samples, a change request form and a prior approval clause in your contract. Add an inspection that compares weights and parts on every reorder, and you can catch changed products before they reach consumers.

There is one thing you can do right now. Open the BOM for the next product you plan to reorder and check whether the manufacturer and model of each main part are listed. If they are not, fill them in first and have the factory confirm them.

GreenFrog Seoul supports you on the ground in China, from organizing spec sheets and BOMs and managing approved samples to designing change approval processes and running teardown comparisons on reorders. If you have already received a changed product, we can start by sorting out the scope of the change and who is responsible. If you are preparing a new order, we can start with the change management clauses to put in your contract.