421-7787 NH3 Ammonia Sensor for CAT Tier 4 Final
Tax calculated at checkout · USD · Free 60-day returns
- 421-7787
What this part is
Buy replacement 421-778701 NH3 Ammonia Sensor for CAT Tier 4 Final (OE 421-778701). Fits CAT Tier 4 Final. 12-month warranty, 60-day returns, free shipping over $99. SKU: 421-778701.
421-7787 NH3 Ammonia Sensor for CAT Tier 4 Final. Single-unit retail NH3 ammonia sensor for SCR aftertreatment, from AutoSensor Tech. Match by the OE number printed on your old part — not by the part name alone.
Fitment & Compatibility
Direct replacement for: CAT Tier 4 Final.
Interchangeable with OE part numbers: 421-7787, 28406016.
Technical Specifications
| Primary OE Part Number | 421-7787 |
| Cross Number | 28406016 |
| Brand / Platform | CAT |
| Application | CAT Tier 4 Final |
| Product Type | NH3 Ammonia Sensor |
| Condition | Aftermarket cross-reference replacement |
| Warranty | 12 Months |
| Shipping | Free over $99 · Same-day dispatch before 14:00 ET |
Photos: front photo is the featured image, back photo is in the gallery. Supplied photos are about 200 px wide, suitable for listing and identification, not for high-resolution zoom. The photos show the module only — confirm whether probe/cable is included before ordering.
Not sure it fits? Send your VIN for a free fitment check before ordering.
Assembly Video
Technical specifications
| Same | day dispatch before 14 |
|---|---|
| not for high | resolution zoom. The photos show the module only |
Identification
| SKU | 421-7787 |
|---|---|
| Category | Caterpillar |
Verified fitment
Send us your VIN and we will confirm fitment within 4 business hours.
12-month parts warranty
Every part ships with a 12-month warranty from the date of delivery. If the part fails under normal use within that window, we replace it or refund the purchase price — your choice.
What we cover
- Manufacturing defects — no questions asked.
- Early failure within the warranty period.
- Replacement shipping both ways, on us.
What we do not cover
- Damage from incorrect installation.
- Parts modified, disassembled, or used in racing.
- Cosmetic wear or normal ageing.
Shipping rates
| Destination | Carrier | Delivery | Cost |
|---|---|---|---|
| United States (cont.) | UPS / USPS | 2–4 biz days | Free $99+ · $6.90 |
| European Union | DHL / DPD | 3–6 biz days | Free $99+ · €8.90 |
| UK / Switzerland | DHL | 3–5 biz days | Free $99+ · £8.00 |
| Rest of world | DHL Express | 5–10 biz days | Calculated at checkout |
Returns
60-day no-fuss returns. Order a return label from your account, drop the part at any carrier drop-off, and we refund within 5 business days of receiving it. Wrong-fit returns are always free.
Returns policy
