A new part number doesn't necessarily mean new tooling. However, you are correct in saying that it is a way to cut cost by not issuing a new part number. A new part number means:
- Entirely new release/approval cycle. That means going through design, release and QA stages (QA is extremely expensive in automotive industry). Remember auto industry is not the software industry, there is no "agile" - waterfall is king because once the product is released, it is infinitely more expensive to change it
- Recalling old part numbers and shipping new ones
- Even the cost of printing new labels and making new packing materials can be non-insignificant
That said, a change in part equals a new part number, period. So, this was very likely a coverup AND an improper cost-reduction exercise.
- Entirely new release/approval cycle. That means going through design, release and QA stages (QA is extremely expensive in automotive industry). Remember auto industry is not the software industry, there is no "agile" - waterfall is king because once the product is released, it is infinitely more expensive to change it
- Recalling old part numbers and shipping new ones
- Even the cost of printing new labels and making new packing materials can be non-insignificant
That said, a change in part equals a new part number, period. So, this was very likely a coverup AND an improper cost-reduction exercise.