P0804 — 1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P0804 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the 1-4 upshift (skip shift) lamp control for damage, corrosion, chafing or poor contact.
Subsystem check Run the module's actuator test for the 1-4 upshift (skip shift) lamp control if your scanner supports it — a component that does not respond to a direct command is confirmed faulty.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P0804 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0804 (parts and labor, USD, independent shop rates): Replace the faulty sensor or actuator: $150–$500; Repair wiring or connectors: $80–$250; Control module repair: $300–$1,000. Overall, fixing P0804 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What are the symptoms of P0804?

Drivers most often notice: the affected system operates intermittently or not at all, Check Engine Light on, possible limp mode depending on the affected component, increased fuel consumption in some cases.

What is the most common cause of P0804?

The most common causes are: faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector, blown fuse feeding the circuit.

How much does it cost to fix P0804?

Replace the faulty sensor or actuator — $150–$500; Repair wiring or connectors — $80–$250; Control module repair — $300–$1,000. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What does OBD2 code P0804 mean?

1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction (P0804): a powertrain (engine/transmission) fault affecting the sensor and actuator circuits. The car is usually drivable while you plan the repair. Most often caused by faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector, blown fuse feeding the circuit.

How do I diagnose P0804 myself?

Start with a scan: confirm P0804, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the 1-4 upshift (skip shift) lamp control, and verify the suspect component against live data before buying parts.

The 1-4 upshift feature, sometimes called skip-shift, is a fuel-saving transmission function found on certain manual and automated manual transmissions. When conditions are right, the transmission control module briefly locks out second and third gear, forcing the driver to shift directly from first to fourth. This reduces engine load during low-speed acceleration. The skip-shift lamp on the dashboard tells the driver when this condition is active. The control circuit for that lamp is what P0804 monitors. When the powertrain module runs its self-test on this circuit, it expects specific voltage patterns and behavior. If the readings do not match what the factory software considers normal, P0804 is stored.

P0804 means the engine or transmission control unit has detected that the 1-4 upshift lamp control circuit is not behaving as it should. The official definition reads "1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction," which places it in the powertrain fault category. This is not a straightforward electrical open or short. A general malfunction code tells you that the fault could be inside the lamp component itself, in the wiring between the module and the lamp, or even in the control module's own driver circuitry that operates the lamp. That is why electrical checks always come before replacing expensive parts.

One thing worth knowing: the module will not set P0804 after a single bad reading. The fault condition must repeat under specific operating parameters before the check engine light comes on and the code is saved. The freeze frame data recorded alongside P0804 captures engine load, RPM, coolant temperature, and vehicle speed at the moment the problem occurred. Those details matter. They let you reproduce the exact driving conditions during testing, which makes diagnosis faster and more accurate.

Common Symptoms of P0804

The Check Engine Light is illuminated and stays on
The skip-shift lamp fails to turn on when it should, or stays on continuously when it should be off
The 1-4 upshift feature does not function at all during the relevant driving conditions
The vehicle may enter a limited-performance mode on some applications, depending on how the manufacturer programs the transmission
Fuel consumption may increase slightly if the transmission cannot execute the skip-shift logic properly
In rare cases, other transmission behaviors may feel slightly irregular until the issue is resolved

Common Causes of P0804

The skip-shift indicator lamp itself has failed internally
An open circuit, short circuit, or damaged wiring in the lamp control circuit
Corrosion, looseness, or physical damage at the electrical connector for the lamp or its associated sensors
A poor ground connection affecting the lamp circuit
The transmission or powertrain control module has developed an internal driver fault or requires a software calibration update
The sensor or actuator that feeds information to the control module for the skip-shift function is malfunctioning

How to Diagnose P0804

Connect an OBD2 scanner and confirm that P0804 is the stored code. Save the freeze frame data before doing anything else — it shows engine load, RPM, coolant temperature, and vehicle speed when the fault was detected. Use those conditions as your test targets.
Check for any other stored codes. Related faults in the same circuit often point to the root cause. Look up manufacturer TSBs for your specific make, model, and year — many P0xxx codes have known factory fixes or software updates.
Inspect the wiring harness and connectors tied to the skip-shift lamp control. Look for chafed insulation, broken strands inside wires, corrosion on pins, and any connectors that are not fully seated.
If your scan tool supports actuator tests, command the skip-shift lamp on and off directly. A lamp that does not respond to a clear electronic command is almost certainly faulty.
Check for proper voltage supply, solid ground, and clean signal at the lamp connector using a multimeter. Compare your readings to what the manufacturer service data specifies.
Perform a wiggle test on the harness while monitoring live data. Any signal dropout during movement points to a broken wire that is only making intermittent contact.

Repair Options and Costs

The right fix depends entirely on what the diagnosis reveals. Working from the cheapest and most common issues first saves money and time.

Repair or replace damaged wiring and corroded connectors in the skip-shift lamp circuit: parts and labor run $80–$250
Replace the faulty sensor, actuator, or the lamp assembly itself: parts and labor range from $150–$500
Reflashing or replacing the powertrain or transmission control module if it is the source of the fault: $300–$1,000

Most P0804 repairs fall somewhere between $80 and $500. The control module route is the least common scenario but represents the upper end of the cost range. Getting a solid diagnosis before purchasing any parts is the single best way to keep total costs down.

Driving Safety Verdict

P0804 is classified as low severity for most drivers. The vehicle remains drivable, though the skip-shift lamp may not work and some transmission functions could be limited depending on the make and model. If the car runs normally in all other respects, scheduling a repair within a reasonable timeframe is appropriate. However, if you notice stalling, failure to start, or any warning lights beyond the check engine indicator, treat it as urgent and have it looked at immediately.