2025 Ram 1500 P0300 Only After an Overnight Soak? Check PCM Software
P0300 Only On The First Cold Start?
Before the first start of the day, record ambient temperature, soak time, fuel level and a short video of the first minute. Save P0300 freeze-frame and misfire data. If the roughness occurs only on the initial start after a long soak, the truck is a 2025 DT with the 3.6L eTorque engine, and normal diagnosis finds no other active cause, Stellantis directs a PCM update. During the flash, voltage must stay between 13.2 and 13.5 volts.
If the cold-soak pattern and software branch match, the equipment needed during the repair is a regulated programming power source, not a spark-plug tester. An AUTOOL EM355 can support a compatible flash setup. EM355 can provide stable low-voltage power for compatible ECU programming when its current output, cables and settings meet the OEM operation; it cannot run wiTECH, decide that software caused the misfire, maintain Stellantis’s voltage window automatically in every setup or replace coil, injector, compression and air-leak diagnosis when evidence points elsewhere.
The best evidence exists before the truck has run for sixty seconds. Once the engine warms and smooths out, repeated restarts cannot recreate an overnight soak; that makes the owner’s first-start record central to a correct software decision.
Quick answer: Capture the first minute after a true overnight soak, exclude conflicting misfire evidence and hold 13.2–13.5 volts if the matched PCM update is performed.
In this guide
- Capture the first minute before it warms up
- Save P0300 freeze-frame and cylinder counters
- Confirm the 3.6L eTorque application
- Separate one cold event from an all-day misfire
- Complete normal diagnosis for conflicting evidence
- Read the current PCM software level
- Hold 13.2–13.5 volts during the flash
- Repeat an overnight soak before closing the case
Capture the first minute before it warms up
Park the truck where the first start can be recorded safely. Before touching the pedal, note the overnight hours, ambient temperature, fuel level and whether a block heater was used. Start normally and film the tachometer sound and dashboard for the first minute. Record how many seconds the roughness lasts and whether it disappears completely. Do not hold the engine at high rpm to smooth it out. If the MIL flashes, the engine knocks or the shake is severe, shut down and arrange inspection rather than repeating the test the next morning.
Save P0300 freeze-frame and cylinder counters
Save P0300 status and freeze-frame before clearing it. Review cylinder misfire counters, coolant and intake-air temperature, cranking voltage, fuel trims and any companion codes. The bulletin names P0300, but evidence that consistently singles out one cylinder, shows low fuel pressure, air leakage or an electrical fault may require a different path. Print the complete scan rather than reporting only ‘random misfire.’ If the battery was recently disconnected or software was changed, include that history because learned values and monitor state can affect what appears on the first start.
Confirm the 3.6L eTorque application
TSB 18-077-26 is for a 2025 Ram 1500 DT with the 3.6-liter V6 24-valve VVT eTorque engine, sales code ERG, in the listed market. Verify VIN, engine and current bulletin revision in DealerCONNECT. A Hurricane-engine truck, a different model year or a misfire that does not match the soak pattern cannot inherit this software repair. Check whether an associated rapid service update is open by VIN and whether the PCM already carries the latest level. Similar dashboard wording is not applicability.
Separate one cold event from an all-day misfire
The defining complaint is rough running on the initial cold start only after an overnight or extended soak. If it continues warm, returns at every idle, appears only under load or follows one cylinder, reopen the mechanical, ignition, fuel and air paths. Compare the coolant and intake temperatures with ambient before starting; an implausible sensor can imitate a cold-calibration problem. A useful work order states what happens on start one and what does not happen on starts two and three. That contrast is more diagnostic than the adjective ‘rough.’
| Pattern | Direction |
|---|---|
| Rough only on first start after long soak, P0300, correct 3.6L DT | Check current PCM calibration and TSB branch |
| Misfire continues warm or follows one cylinder | Continue ignition, fuel, air and mechanical diagnosis |
| PCM already at latest level | Do not repeat the same flash by guess |
| Update completed | Verify after another true overnight soak |
Complete normal diagnosis for conflicting evidence
Use wiTECH with the current diagnostic procedures to verify related systems operate as designed. Check active and stored faults, battery condition, obvious vacuum or intake problems, fuel quality and any cylinder-specific evidence. Do not install coils, plugs or injectors merely to see whether the first-start event changes. Conversely, do not use the bulletin to wave away coolant loss, low compression or a flashing MIL. The software branch becomes strong only when model, engine, soak-only behavior and lack of conflicting evidence all agree.
Read the current PCM software level
Read and save the current PCM part and software information before the flash. Confirm the latest calibration is available for that VIN and follow the wiTECH prompts. Stable wired connections and current credentials matter. A consumer code reader cannot install the update, and clearing P0300 does not change calibration. If the vehicle is already current, document that fact and return to normal diagnosis rather than reflashing the same level. If programming fails, use the factory recovery process instead of cycling the ignition repeatedly.
Hold 13.2–13.5 volts during the flash
Stellantis specifies a charger so voltage does not fall below 13.2 volts and does not rise above 13.5 volts during this flash. Set up approved support, turn off accessories and monitor the vehicle—not merely the charger’s display. Cables need secure clean contact and adequate capacity. Do not use an uncontrolled booster or leave the engine running. Programming can command modules awake and change load; a power source suitable for ordinary battery charging may not be stable enough. Save the post-flash software identity and the DTC report presented by wiTECH.
Repeat an overnight soak before closing the case
Clear the codes set by programming as instructed, but do not call a warm restart the verification. The truck must cool and sit through the same overnight or extended interval that produced the complaint. Repeat the first-start video with similar ambient conditions and compare roughness duration, rpm and misfire counters. If P0300 or the shake returns, reopen the diagnostic evidence instead of repeating the update. Give the owner both software levels and before/after cold-start records so the resolution is tied to the symptom they actually experienced.
This Ram complaint is solved at dawn, not after an afternoon of warm restarts. Preserve the first minute, prove the exact 3.6L eTorque scope and exclude evidence that points to a real cylinder or system fault. Stop the test and arrange inspection if the MIL flashes, the engine knocks or the shaking becomes severe. If the software branch matches, use wiTECH with voltage held inside 13.2–13.5 volts, then wait for another genuine soak. That sequence gives the owner an answer to the problem they reported and keeps unnecessary ignition parts out of the story.
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