P0888 OBD-II Trouble Code: Transmission Relay Sense Circuit (or Relay Output Always Off)

P0888 code definition

The P0888 code is the universal code for Transmission Relay Sense Circuit (or Relay Output Always Off). Co-occurring or alternative codes may be P0869, P0871, P0876, or any of P0885 – P0892.

What the P0888 code means

P0888 is the OBD-II trouble code indicating a problem with the transmission control relay or else somewhere in the related circuitry. The transmission control relay supplies power to the solenoid pack when the transmission is functioning properly. This code is thrown when fewer than three volts are present at the transmission control relay output terminals of the PCM (powertrain control module) as the PCM is energizing the relay.

What causes the P0888 code?

A transmission control power relay sense circuit problem can be caused by a number of malfunctions:

• A faulty TCR (transmission control relay)
• An open TCR output circuit
• A short in the TCR control or output circuit
• A faulty PCM (powertrain control module)
• A faulty connection within the circuit
• A faulty transmission solenoid/pressure switch assembly

What are the symptoms of the P0888 code?

When a vehicle is storing this code, it will likely cause the Check Engine Light to come on, and can potentially result in the vehicle only operating in “limp” mode, failing to switch gears. Some people also experience a loss of A/C power.

How does a mechanic diagnose the P0888 code?

P0888 is diagnosed by hooking an OBD-II scanner to the vehicle’s port. The technician will then document freeze frame data, determine when the code set along with any concurring codes, and then clear the vehicle’s computer of the data and test drive it to see if the code returns.

During the road test, the mechanic should observe the sensor’s live data. If the code does return, the wiring, PCM connector, and relay contacts should be visually examined. If these are not the apparent cause of the problem, he or she may use a multimeter to test the circuit according to the manufacturer’s pinpoint tests.

Common mistakes when diagnosing the P0888 code

The most common errors when diagnosing this code occur when the proper steps are not followed to find the root of the problem. There is a temptation to simply flash the TCM or replace the TCR or transmission solenoid without making sure the voltage is correct throughout all of the involved circuitry.

How serious is the P0888 code?

This fault code can be very serious if it is causing the vehicle to operate in limp mode. Vehicles in limp mode should not be driven except to get to the nearest shop. If your vehicle shows this code, you should have a qualified technician address the problem as soon as possible to prevent further damage.

What repairs can fix the P0888 code?

The most common potential repairs to address the P0888 code are as follows:

• Check to make sure the code returns after all codes have been cleared and the vehicle driven again.
• Inspect the TCR to ensure it’s working and that the ground is not faulty.
• Visually inspect all wiring and connectors.
• Ensure that there is no 12-volt signal at the transmission control module, indicating an open circuit.
• Inspect input and output sensors for dirt and grime. Use contact cleaner if necessary.
• Replace TCR if necessary.
• Replace TCR harness if necessary.
• Replace transmission solenoid/pressure switch assembly if necessary.

Additional comments for consideration regarding the P0888 code

Identifying and repairing P0888 can be a very complex, involved repair which is beyond the scope of most home mechanics. Advanced electrical skill is generally required, and the ability to examine multiple small, specific parts, as there are several possible causes, most requiring testing of voltage between certain components. If possible, it’s best to have a trained automotive technician diagnose and fix this code as soon as you notice a problem.

Need help with a P0888 code?

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