Damaged, chafed or corroded wiring in the vehicle speed output circuit (open circuit, short to earth or short to voltage); Poor connection or corrosion at the engine control module, instrument cluster or related connectors; Faulty vehicle speed sensor or its signal supply, giving the module a bad input to process; Fault in the instrument cluster or another module that receives the speed signal, loading or disturbing the circuit; Internal fault in the engine control module output driver; Aftermarket accessories or poor previous repairs tapped into the speed signal wiring.

P1504

Vehicle Speed Output Circuit.

Oldsmobile
Powertrain
Manufacturer code
Low severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
5: AreaVehicle speed, idle control and auxiliary inputs
04: FaultThe specific fault in that area

What it means

P1504 on an Oldsmobile means the engine control module has detected a fault in the vehicle speed output circuit. This is the signal the module sends to other systems, such as the instrument cluster, cruise control or other modules, after processing the road speed input. The module saw the output signal missing, shorted or not matching what it commands, so it set the code.

Symptoms

Speedometer reads wrong, jumps about or does not work
Cruise control not working or dropping out
Check engine light on
Erratic or harsh transmission shifting on some models
Odometer or trip meter not counting
Poor idle or stalling when coming to a stop on some models

Possible causes

Damaged, chafed or corroded wiring in the vehicle speed output circuit (open circuit, short to earth or short to voltage)likely
Poor connection or corrosion at the engine control module, instrument cluster or related connectorslikely
Faulty vehicle speed sensor or its signal supply, giving the module a bad input to processpossible
Fault in the instrument cluster or another module that receives the speed signal, loading or disturbing the circuitpossible
Internal fault in the engine control module output driverrare
Aftermarket accessories or poor previous repairs tapped into the speed signal wiringrare

How to diagnose

Read all stored codes and freeze frame data, and note whether any speed sensor, transmission or cluster codes are also present
Check the speedometer and cruise control operation on a road test to see exactly what is affected
Visually inspect the speed signal wiring and connectors for chafing, water ingress, corrosion and pushed-out pins
Check for any aftermarket wiring or devices connected to the speed signal circuit
Use the wiring diagram for the specific model to identify the output circuit, then test for continuity, short to earth and short to voltage with the module disconnected
Check the supply, earth and signal from the vehicle speed sensor, and compare the live speed reading with actual road speed
Check the signal arriving at the receiving device, such as the cluster, to confirm whether the fault lies in the wiring, the module or the receiver
Clear the code and recheck to see if it returns before condemning the control module

How to fix

Repair or replace damaged wiring in the speed output circuit
Clean, repair or replace corroded or loose connectors and terminals
Replace the vehicle speed sensor if its signal is faulty
Repair or replace the instrument cluster or other receiving module if it is found to be loading the circuit
Remove faulty aftermarket wiring and restore the original circuit
Replace or repair the engine control module only after wiring and receivers have been proven good, and have it programmed as required for the model

Can I keep driving?

Low severity

The car can usually be driven while you book it in, but an inaccurate speedometer and lost cruise control may affect safe and legal driving. Have it checked soon, especially if shifting or idle is also affected.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.