Buy for what you actually do. A $20-30 Bluetooth dongle reads and clears powertrain codes and shows basic live data — enough for a stock daily driver. A $150-250 bidirectional scanner adds ABS, airbag, and body-module coverage plus active tests, which is what earns its money on a truck you take past cell service. Before you buy anything for a 2018-or-newer truck, understand the Security Gateway below, because it decides whether your tool can command anything or only read. The codes you will actually see are misfires (P0300 plus a cylinder number), catalyst efficiency (P0420/P0430), and EVAP leaks (P0455/P0456). Read the freeze frame, fix the root cause, re-scan — clearing a code without fixing the cause resets the clock, nothing else.
Starting with the 2018 model year, FCA began fitting a Security Gateway Module (SGW) to Ram trucks. It sits between the OBD-II port and the vehicle's internal buses. Reading codes and live data still works normally through it. What the SGW blocks is writes: bidirectional commands, active tests, module programming, key programming, and some ABS bleed routines from tools that have not authenticated.
Three ways around it, in order of how sane they are:
If a tool you own suddenly cannot run an active test that worked on an older vehicle, the SGW is almost always why.
P0300, P0301-P0308 — random or cylinder-specific misfire. On the 6.4L the order of suspicion is worn spark plugs first (16 of them, two per cylinder), then a failing coil-on-plug, then injector or compression problems. The classic confirmation: swap the suspect coil with a neighboring cylinder's, clear the code, and drive. If the misfire follows the coil, you found it. If it stays with the cylinder, look at the plug, injector, then compression.
P0420 / P0430 — catalyst efficiency below threshold. Frequently an aging downstream O2 sensor rather than a dead converter. Test before you spend converter money; a scan tool that graphs upstream versus downstream O2 activity settles it in a few minutes.
P0455 / P0456 / P0457 — EVAP leak, large to small. Start with the fuel cap and its seal, then the purge and vent solenoids. P0457 explicitly points at the cap or a loose fuel-fill component.
P0344 / P0339 — cam or crank position sensor signal. Often intermittent, often heat-related, and a common cause of a no-restart after the truck sits hot.
U0100-family codes — module communication loss. Before condemning a module, check battery voltage and the chassis grounds. A weak battery or a corroded ground causes more U-codes than failed modules do, and on an accessorized truck a poorly grounded aftermarket circuit is a frequent culprit.
Codes referencing cylinder deactivation on the trucks that have it generally trace back to oil pressure, lifters, or solenoids rather than to the electronics.
Address the root cause, clear the codes, then drive the truck through several drive cycles so the readiness monitors re-run. A cold start, a period of steady cruise, and some stop-and-go over a few days is usually enough; EVAP monitors are the fussiest and often need a specific fuel level, roughly a quarter to three-quarters of a tank, plus a cold soak.
A code that returns immediately means the fault is still live. A code that stays gone through a full cycle with monitors reporting complete is fixed. For misfire codes, move to the spark plug and coil guide; for fuel delivery and pressure codes, the fuel pump guide covers the pressure test.
Codes tell you what already broke. Live data warns you before it does. On a loaded climb or a long low-range crawl, keep these on screen:
| PID | Watch for | Why |
|---|---|---|
| Transmission temperature | Sustained above ~220°F; back off well before ~250°F | The 66RFE six-speed on 2014-2018 trucks and the eight-speed on later 6.4L trucks both cook fluid under low-range load — confirm which you have by year |
| Coolant temperature | Creep above the normal operating band | Catches a lazy fan clutch or a fouled radiator early |
| Short/long-term fuel trims | Drift positive at idle | Vacuum or intake leak |
| Battery / charging voltage | Sag under winch or light load | Catches a failing alternator on a winch-heavy day |
| Misfire counters per cylinder | One cylinder climbing | Lets you back off before it sets a hard code miles from pavement |
Cross-check coolant behavior against the baseline in the cooling system guide, and if you are running a winch and accessories, the alternator guide covers what the charging system can actually support.
| Tier | Cost | What it does | Notes |
|---|---|---|---|
| ELM327 Bluetooth dongle + app | $20-30 | Read/clear powertrain codes, basic live data | Avoid the cheapest clones — they drop connection and misread Chrysler-specific PIDs |
| OBDLink MX+ / BlueDriver | $100-140 | Reliable link, enhanced FCA codes, good logging | The sweet spot for an owner who is not doing module work |
| Autel MK808-class / Launch CRP-class | $150-300 | All modules, active tests, service resets | Confirm FCA SGW support for your exact model on 2018+ trucks |
| Shop-grade bidirectional | $400+ | Full bidirectional, programming | Only worth it if you are working on several vehicles |
Buy the tier above the dongle if you go off pavement. Watching trans temp climb once, in time to stop and let it cool, pays for the tool.
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.
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