3 of 7 open
ALR-2188·Critical·Diagnostic trouble code·opened May 4 · 18:14 by system
Catalyst efficiency below threshold — P0420
Detected on Sprinter #29 while operated by Rosa Patel on the Eastside route.
Driver at detection
RP
Rosa Patel
DRV-014
First detected
May 4 · 18:14:02
2 days, 4h ago
Last seen
today · 12 min ago
re-occurred 3 trips
Description
The vehicle's primary three-way catalytic converter is no longer reducing post-combustion hydrocarbons to within the OEM-defined efficiency window. The post-cat oxygen sensor reading is closely tracking the pre-cat sensor — the signature of a catalyst that has lost its conversion capacity.
P0420 typically develops over time on diesel platforms with high mileage and frequent short-duty cycles. Less commonly, it indicates a failed post-cat O2 sensor, an exhaust leak upstream of the sensor, or upstream cylinder misfires fouling the substrate. P0301 (cylinder 1 misfire) was logged 7 days prior on this vehicle and may be contributing.
Telemetry that triggered the alert
O2 sensor voltages, pre-cat (B1S1) vs post-cat (B1S2). Healthy catalyst → B1S2 should be stable; here it tracks B1S1.
B1S1 · pre-catB1S2 · post-catExpected B1S2 envelope
06:14
06:46
07:18
07:50
08:22
08:54
Service recommendation
Replace primary catalytic converter and bank-1 post-cat O2 sensor
During service, inspect cylinder 1 coil and injector for related P0301 misfires. Estimated $1,420 parts & labor at Northgate Diesel · 4–6 hours.
Continue driving?
Yes — short trips only. Avoid sustained loads.
Emissions impact
Will fail next WA inspection (Aug 14)
Risk if ignored
Cascading post-cat sensor failure within ~2k mi
Prior occurrences P0420 across the fleet
| Vehicle | First seen | Resolved | Resolution | Cost |
|---|---|---|---|---|
| Sprinter #29 · this alert | May 4, '26 | Open | In service at Northgate | est. $1,420 |
| Transit #4 | Jan 22, '26 | Feb 2, '26 | Catalyst replaced | $1,308 |
| F-250 #18 | Aug 11, '25 | Aug 18, '25 | Post-cat O2 sensor replaced | $184 |
| Sprinter #29 | Apr 3, '24 | Apr 9, '24 | Catalyst replaced (under warranty) | $0 |