Failed skip-shift solenoid, often due to an open or shorted internal coil; Damaged or corroded wiring harness between the PCM and the solenoid; Loose or corroded electrical connector at the solenoid or PCM; Blown fuse or faulty relay supplying power to the solenoid circuit; Internal PCM driver failure, though this is less common; Aftermarket tuning or programmer that has disabled the skip-shift function; Mechanical binding in the shift mechanism that prevents the solenoid from moving

DTC codes / P08xx · Transmission / P0804

P08041-4 Upshift (Skip Shift) Lamp Control Circuit

Q: What does code P0804 mean?

1-4 Upshift (Skip Shift) Lamp Control Circuit. P0804 indicates that the powertrain control module has detected a fault in the control circuit for the skip-shift solenoid, which forces a 1-to-4 gear change under light throttle to save fuel. The computer monitors the circuit for abnormal voltage or current and sets this code when the signal does not match expected values.

P0804 indicates that the powertrain control module has detected a fault in the control circuit for the skip-shift solenoid, which forces a 1-to-4 gear change under light throttle to save fuel. The computer monitors the circuit for abnormal voltage or current and sets this code when the signal does not match expected values.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaTransmission

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
The skip-shift feature may stop working, allowing normal 1-2-3-4 shifting
In rare cases, the transmission may stay in first gear or refuse to upshift
A slight decrease in fuel economy if the skip-shift system is disabled
Possible harsh engagement when shifting from first to fourth if the solenoid sticks
No drivability complaints in most cases because the system is emissions-related

Common causes, most likely first

Failed skip-shift solenoid, often due to an open or shorted internal coil
Damaged or corroded wiring harness between the PCM and the solenoid
Loose or corroded electrical connector at the solenoid or PCM
Blown fuse or faulty relay supplying power to the solenoid circuit
Internal PCM driver failure, though this is less common
Aftermarket tuning or programmer that has disabled the skip-shift function
Mechanical binding in the shift mechanism that prevents the solenoid from moving

How to diagnose and fix it

Use a scan tool to confirm P0804 is active and check for related transmission codes
Inspect the solenoid connector and wiring for corrosion, chafing, or loose pins
Test the solenoid resistance with a multimeter and compare to manufacturer specification
Check the fuse and relay that supply power to the skip-shift circuit
Perform a voltage drop test on the ground and power sides of the circuit under load
If the circuit tests good, command the solenoid on with a scan tool to verify operation
Replace the solenoid or repair wiring as needed, then clear codes and verify the repair

Skip-shift solenoid diagnosis pitfalls

Many technicians replace the solenoid only to find a chafed wire behind the engine block that was the real cause of the circuit fault.
A skip-shift solenoid that tests good cold can fail intermittently when hot, so a resistance check alone may not confirm a faulty part.
Some aftermarket handheld tuners disable the skip-shift feature and can set P0804 as a side effect, so check for non-stock calibration first.
The PCM driver for this circuit can be damaged by a shorted solenoid, so always check for a short to ground before installing a new PCM.
This code is often stored alongside P0803, which points to the same circuit but a different failure mode, so review all codes before diagnosing.

Can I keep driving with P0804?

The vehicle remains safe to drive because the skip-shift system only affects fuel economy and emissions, not basic transmission operation. Avoid aggressive acceleration if the transmission feels stuck in first gear, and have the circuit inspected soon to prevent further electrical damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.