P1604 means the ECM judged that the engine failed to start normally; it is an outcome code, not a starter or fuel-pump verdict. Reconstruct slow crank, normal-speed no-fire or start-then-stall. Test battery/cranking voltage and speed, cam/crank synchronization, immobilizer authorization, actual fuel/pressure, ignition, MAF/throttle/purge and compression. Toyota flex-fuel P1604 bulletins for Tundra/Sequoia do not list Tacoma.
Match the symptom
Select the closest observation. The result changes the first test; it does not name a part to replace.
Test battery and voltage drop at starter/grounds.
What can set P1604—and how to separate it
The order below is evidence-driven, not a universal probability ranking. Vehicle year, repair history, companion codes and the operating condition in freeze frame change where diagnosis should begin.
| Possible cause | Evidence that supports it | First useful test |
|---|---|---|
| Weak battery, starter or cable voltage drop | Low cranking speed/voltage or hot connection | Battery load and cranking voltage-drop tests |
| Fuel quantity/quality/pressure or injector fault | No/low pressure or contaminated fuel | Verify actual fuel and engine-specific delivery |
| Crank/cam signal, ignition or immobilizer fault | No rpm/sync/spark or authorization abnormal | Companion codes and start-authority data |
| Airflow, throttle or purge flooding | Post-refuel stall or implausible intake data | Inspect air path and purge sealing |
| Compression or mechanical timing fault | Uneven cranking, noise or correlation code | Relative compression and timing checks |
Startability is an outcome, not a component
Slow cranking prioritizes the battery/starter path. Normal cranking without firing prioritizes synchronization, authorization, fuel and ignition. Starting then stalling moves purge, throttle and security higher.
Write the pattern and temperatures down before charging the battery or cooling the engine.
Truck electrical modifications matter
Winches, dual-battery systems, grounds, remote start and auxiliary wiring can introduce voltage drop or authorization problems. Inspect changes without assuming they are guilty.
Measure voltage at the relevant component during the event; an open-circuit battery reading cannot prove cranking performance.
Reject the wrong flex-fuel bulletin
Search results may pair P1604 with Tundra/Sequoia alcohol-density calibration. Applicability is part of the evidence, and Tacoma is not listed.
Use VIN-correct Tacoma TIS and actual failed-start data. Similar code numbers do not make models interchangeable.
Save these scan-data clues
Freeze frame is a snapshot of conditions when the PCM matured the fault. It can distinguish an idle-only problem from a load, cold-start or monitor-completion problem. Clearing first throws that context away.
- Minimum cranking voltage and rpm
- Cam/crank synchronization
- Start authorization/immobilizer status
- Fuel level, pressure and injector command
- MAF/MAP/throttle and purge data
- Hot/cold, remote-start and recent service history
A practical diagnostic workflow
- 01Name the start pattern
Record slow crank, no-fire or start-then-stall.
- 02Save all codes
Companion codes outrank the outcome code.
- 03Measure cranking quality
Test voltage, speed and cable drop.
- 04Verify sync and authorization
Confirm ECM receives required signals.
- 05Test fuel, ignition, air and compression
Follow the missing prerequisite.
- 06Verify hot and cold starts
Confirm normal duration with no pending P1604.
Do not replace the starter, fuel pump or ECM from P1604 alone. Tundra/Sequoia alcohol-density bulletins do not apply to Tacoma merely because the code matches.
Why the model year changes the test
Tacoma diagnostics span older 2RZ/3RZ and 5VZ engines, the long-running 2TR-FE four-cylinder and 1GR-FE V6, 2016–2023 2GR-FKS V6, and 2024+ turbocharged T24A-FTS including i-FORCE MAX. Engine, bank layout, fuel system, EVAP routing, VVT strategy and bulletin coverage differ. Confirm model year, VIN, engine code, drivetrain and emissions label before choosing tests.
- P1604 is Toyota-enhanced; Toyota-capable data may expose start-history detail absent from basic readers.
- T-SB-0166-19 and predecessor list flex-fuel Tundra/Sequoia, not Tacoma.
- Remote-start/security additions and off-road battery accessories can alter cranking/authorization and should be disclosed.
- 2024+ turbo/hybrid starting and fuel systems require their own procedures.
P1604 FAQ
What does P1604 mean?+
The ECM detected abnormal or unsuccessful starting performance.
Is the starter bad?+
Not automatically; many prerequisites can be missing.
Can a weak battery set it?+
Yes, through inadequate cranking voltage or speed.
Can running out of fuel set it?+
A failed start from insufficient fuel can contribute.
Do Tundra bulletins apply?+
No, not unless Tacoma is listed—which those flex-fuel bulletins do not.
Can remote start matter?+
Accessory wiring or authorization issues can change starting behavior.
Should I clear it first?+
No. Save failed-start data and companion codes.
What proves repair?+
Reliable hot/cold starts and no pending return.
Ford diagnostic references
These documents explain Ford monitor operation. Exact pinpoint tests, connector views and specifications must be selected for the truck's VIN and model year in current service information.
01Toyota Tacoma manuals and warranty guidesOfficial Toyota model-year document lookup; use VIN-, engine- and drivetrain-correct Toyota repair information↗