P0874 Transmission Fluid Pressure Sensor / Switch "C" Circuit Intermittent

P0874 is a transmission-related diagnostic trouble code that points to an intermittent electrical problem in the Transmission Fluid Pressure Sensor/Switch "C" circuit.

Unlike a code that simply indicates a pressure value is too high or too low, P0874 tells us that the transmission control system is seeing a pressure-sensor/switch signal that comes and goes, becomes unstable, or temporarily falls outside the expected electrical behavior.

This distinction is extremely important.

P0874 does not automatically mean that transmission hydraulic pressure is intermittently low. The transmission may be producing normal hydraulic pressure while the electrical signal from the sensor or switch is intermittently disappearing or becoming implausible.

The fault may therefore be caused by a sensor, connector, wiring problem, poor terminal contact, power or ground issue, or—in some cases—a genuine hydraulic problem.

Why the Word "Intermittent" Matters

The most useful word in P0874 is actually "Intermittent."

A permanent open circuit is usually relatively easy to locate. An intermittent fault can disappear before the technician begins testing.

For example, the vehicle may:

• Shift normally during inspection

• Have no warning light at first

• Store P0874 as a history or pending code

• Suddenly produce harsh shifting

• Enter limp mode

• Return to normal after the ignition is switched off and on

This behavior is typical of faults affected by temperature, vibration, moisture, harness movement, or connector contact.

The transmission controller has effectively detected:

"The pressure sensor/switch signal was not behaving correctly at some point, but the condition is not necessarily present right now."

What Is Transmission Fluid Pressure Sensor/Switch "C"?

Automatic transmissions rely on hydraulic pressure to control clutches, bands where applicable, valves, and other internal mechanisms.

Pressure sensors and pressure switches allow the transmission control system to monitor hydraulic conditions.

The exact meaning of "C" is not universal.

Depending on the transmission, it may identify:

• A particular pressure sensor

• A pressure switch

• A hydraulic pressure circuit

• A sensor integrated into the valve body

• An internal transmission sensor

• A specific pressure-monitoring channel

Therefore, the location and electrical configuration of Pressure Sensor/Switch "C" must be confirmed using the specific vehicle's service information.

It should not automatically be assumed that Sensor "C" is in the same location on another vehicle.

How P0874 Differs From P0870

P0870 is generally described as:

Transmission Fluid Pressure Sensor/Switch "C" Circuit Malfunction

P0874 adds an important detail:

Transmission Fluid Pressure Sensor/Switch "C" Circuit Intermittent

In practical terms, P0874 suggests that the controller has detected a signal problem that is not consistently present.

That makes wiring, connectors, terminals, heat-related faults, vibration, and intermittent sensor failures particularly important areas to investigate.

However, the two codes can have overlapping causes, and manufacturers may use slightly different monitoring strategies.

Common Symptoms of P0874

The symptoms depend heavily on how the transmission responds when the pressure signal becomes unreliable.

Possible symptoms include:

• Check Engine Light

• Transmission warning message

• Harsh shifting

• Delayed gear engagement

• Erratic shifting

• Transmission slipping

• Gear hunting

• Loss of certain gears

• Limp-home mode

• Increased engine RPM during shifts

• Poor acceleration

• Delayed reverse engagement

• Transmission overheating

• Intermittent transmission malfunction

Some vehicles may show almost no noticeable symptoms.

That does not mean the fault should be ignored. An intermittent pressure-signal problem can eventually become a permanent failure.

The Most Likely Causes

Several different faults can produce P0874.

Pressure Sensor/Switch "C"

The sensor or switch may have an internal electrical fault.

A sensor can work correctly when cold and become unreliable after the transmission reaches operating temperature.

Damaged transmission wiring

Wiring near the transmission is exposed to:

• Heat

• Vibration

• Oil

• Moisture

• Engine and transmission movement

• Physical abrasion

A conductor can break internally while the outside of the insulation still looks perfectly normal.

Loose connector terminal

This is an especially important possibility with intermittent codes.

A terminal can lose its contact tension and intermittently disconnect as the vehicle vibrates.

Corrosion or contamination

Moisture or transmission fluid contamination around a connector can alter electrical resistance and create unstable signals.

Poor sensor ground

A pressure sensor can produce an incorrect signal if its ground circuit becomes unstable.

Reference-voltage problem

If the sensor uses a reference voltage supplied by the transmission controller, problems affecting that reference circuit can alter the pressure signal.

Shared wiring fault

Several transmission sensors may share power, ground, or reference circuits. A fault affecting a shared circuit can therefore produce multiple diagnostic codes.

Internal transmission harness problem

Some transmissions have wiring and sensors inside the transmission itself.

An intermittent internal connection can be considerably harder to identify than an external harness problem.

Hydraulic problem

A genuine hydraulic pressure problem can sometimes cause the pressure sensor signal to behave differently from what the controller expects.

Possible causes include pump problems, valve-body issues, solenoid problems, internal leakage, or incorrect fluid level.

But hydraulic failure should not be assumed simply because P0874 is stored.

Start With Freeze-Frame Data

Because P0874 is intermittent, freeze-frame data can be particularly valuable.

When the code was stored, look at information such as:

• Transmission temperature

• Engine RPM

• Vehicle speed

• Selected gear

• Throttle position

• Battery voltage

• Pressure sensor reading

• Solenoid commands

• Transmission input/output speed

Suppose P0874 repeatedly appears only when the transmission temperature reaches 90°C or higher.

That would make a temperature-sensitive sensor, connector, wiring fault, or internal transmission issue more suspicious.

If it appears primarily during a specific shift, the diagnostic direction may be different.

Do Not Start by Replacing the Sensor

A common mistake with P0874 is to see "Pressure Sensor/Switch C" in the description and immediately replace the sensor.

That can work if the sensor really is defective, but it is not a diagnosis.

An intermittent code can easily be caused by the wiring going to the sensor.

Imagine a sensor has a perfectly good signal when the vehicle is stationary. During acceleration, the engine and transmission move slightly on their mounts. The harness moves with them, a damaged conductor separates momentarily, and the pressure signal disappears.

Replacing the sensor would not fix that problem.

The wiring fault would remain.

Inspect the Connector Carefully

The connector should be examined for more than visible corrosion.

Check for:

• Bent pins

• Loose terminals

• Broken locking tabs

• Water intrusion

• Oil contamination

• Corrosion

• Terminals pushed backward into the connector

• Poor terminal tension

• Damaged seals

A connector may appear clean but still have inadequate terminal contact.

This is one reason intermittent transmission codes can be difficult to reproduce.

Perform a Wiggle Test

When appropriate for the vehicle, monitor the pressure sensor signal while carefully manipulating the relevant harness and connector.

If the signal suddenly changes while the harness is moved, there is strong evidence of an intermittent electrical problem.

The test should be performed carefully.

The objective is not to pull aggressively on the harness but to reproduce the type of movement that may occur during normal driving.

Continuity Testing Is Not Enough

A basic continuity test can show that a wire is connected when the vehicle is stationary.

It cannot necessarily prove that the circuit remains reliable when:

• Hot

• Vibrating

• Under electrical load

• Under mechanical tension

• Exposed to moisture

For this reason, voltage-drop testing, circuit loading, and—where appropriate—oscilloscope testing can provide much stronger evidence.

An oscilloscope is particularly useful when the pressure sensor produces a variable signal and the problem occurs only for a fraction of a second.

Check the Sensor Signal Against Transmission Conditions

If the scan tool provides pressure-related live data, watch the value while driving.

Pay attention to whether the signal:

• Drops suddenly

• Jumps unexpectedly

• Becomes implausible

• Freezes at one value

• Changes when the harness is moved

• Becomes unstable at a particular temperature

• Changes during a particular gear shift

A pressure signal that suddenly becomes impossible while the transmission continues functioning normally is an important clue toward an electrical problem.

Compare Reported Pressure With Actual Pressure

This is where a professional diagnosis becomes much more reliable.

There are potentially three different things to compare:

Commanded pressure

What the transmission controller is requesting.

Reported pressure

What the pressure sensor tells the controller.

Measured hydraulic pressure

What a mechanical pressure gauge actually measures.

These three values should not automatically be assumed to be identical.

If the sensor reports an abnormal pressure but a mechanical gauge shows that hydraulic pressure is normal, the sensor circuit becomes highly suspicious.

If both the electronic reading and mechanical pressure show a genuine pressure problem, the investigation needs to move toward the hydraulic system.

Could Low Transmission Fluid Cause P0874?

It can contribute to transmission pressure problems, but low fluid does not automatically explain an intermittent electrical circuit code.

If fluid is low, determine why.

Possible causes include:

• External leaks

• Axle seal leakage

• Cooler line leakage

• Pan gasket leakage

• Transmission case leakage

• Connector/seal problems

A low fluid level can cause hydraulic pressure problems, aeration, delayed engagement, and slipping.

Therefore, fluid condition should be checked, but it should not be used as a substitute for testing the electrical circuit.

Check the Fluid Correctly

Transmission fluid checking procedures vary considerably.

Some transmissions use a dipstick.

Others require the vehicle to be:

• On a level surface

• At a specified transmission temperature

• Running or stopped according to the manufacturer's procedure

• Checked through a specific fill/check port

The wrong procedure can make a correctly filled transmission appear underfilled or overfilled.

Also verify that the correct fluid specification was used.

Can a Bad Valve Body Cause P0874?

Potentially, yes, but there needs to be supporting evidence.

The valve body controls hydraulic routing inside the transmission, and pressure sensors/switches may be integrated into or associated with it.

A valve-body problem becomes more convincing when P0874 is accompanied by:

• Abnormal mechanical pressure

• Multiple hydraulic pressure codes

• Solenoid-related codes

• Specific shift problems

• Sticking valves

• Pressure abnormalities during particular gear changes

A valve body should not be replaced solely because P0874 is present.

Can a Pressure-Control Solenoid Cause It?

Depending on the transmission architecture, a pressure-control solenoid can influence the hydraulic pressure that the sensor is monitoring.

A malfunctioning solenoid can therefore create a genuine pressure abnormality.

However, the technician should determine whether the solenoid is:

1. Electrically faulty,

2. Mechanically sticking,

3. Being incorrectly commanded,

4. Responding correctly but unable to achieve the requested pressure because of another hydraulic problem.

Those are very different faults requiring different repairs.

Temperature Can Reveal an Intermittent Fault

Heat is one of the most useful clues when diagnosing P0874.

A sensor or wiring connection may behave perfectly at 20°C and fail at 90°C.

As components heat up:

• Electrical resistance can change

• Damaged conductors can expand

• Internal sensor defects can become apparent

• Connector contact can deteriorate

• Transmission fluid viscosity changes

• Hydraulic clearances change

If the code appears only after extended driving, reproduce the fault at operating temperature rather than testing only a cold vehicle.

Look for Related Codes

P0874 should rarely be considered in isolation.

Scan all modules and look for related faults involving:

• Other transmission pressure sensors

• Pressure-control solenoids

• Shift solenoids

• Transmission temperature

• TCM communication

• Battery voltage

• CAN communication

• Gear-ratio monitoring

If several sensors suddenly report electrical problems at the same time, a shared power, ground, reference, connector, or wiring problem becomes more likely.

If only Pressure Sensor/Switch "C" is affected, the investigation can be narrowed toward that circuit.

A Useful Real-World Diagnostic Scenario

Consider a vehicle that drives normally when cold.

After approximately 30 minutes, the transmission begins shifting harshly and P0874 is stored.

The technician checks the fluid level and finds it correct.

The scan tool shows that the pressure signal suddenly becomes implausible when the transmission reaches operating temperature.

A mechanical pressure test, however, shows that actual hydraulic pressure remains within specification.

The problem is therefore unlikely to be a failed transmission pump.

Further inspection finds a transmission connector with a loose terminal.

When the transmission becomes hot and vibrates during shifting, the terminal loses contact momentarily.

The pressure signal disappears, the TCM detects the intermittent circuit condition, and P0874 is stored.

Repairing the terminal fixes the problem.

This type of failure is exactly why intermittent transmission codes should not automatically lead to expensive mechanical repairs.

Another Possibility: Genuine Hydraulic Pressure Loss

Now consider a different vehicle.

P0874 appears together with slipping, delayed engagement, and abnormal pressure readings.

A mechanical gauge confirms that hydraulic pressure genuinely drops during certain operating conditions.

At that point, the sensor circuit may actually be reporting a real hydraulic problem.

The investigation should then move toward:

• Fluid level

• Fluid condition

• Filter restriction

• Pump performance

• Pressure-control solenoids

• Valve-body condition

• Internal leakage

• Seals and clutch circuits

The important difference is that the hydraulic diagnosis is supported by actual measurements.

Is P0874 Safe to Drive With?

If the vehicle drives completely normally and P0874 is an occasional stored code, it may remain operational for a short period.

However, an intermittent fault should not be ignored indefinitely.

If you experience:

• Severe slipping

• Loss of gears

• Delayed engagement

• Harsh engagement

• Transmission overheating

• Limp mode

• Loss of reverse

• Sudden changes in transmission behavior

the vehicle should be diagnosed promptly.

If the transmission is genuinely losing hydraulic pressure, continued operation can generate excessive heat and accelerate internal damage.

What Repairs Can Resolve P0874?

The correct repair depends entirely on the test results.

Possible repairs include:

• Repairing damaged wiring

• Replacing a damaged connector

• Repairing poor terminal contact

• Repairing a sensor ground

• Restoring the correct reference voltage

• Replacing Transmission Fluid Pressure Sensor/Switch "C"

• Repairing an internal transmission harness

• Correcting fluid level

• Repairing a transmission fluid leak

• Replacing incorrect or contaminated fluid

• Servicing the valve body

• Replacing a faulty pressure-control solenoid

• Repairing an internal hydraulic problem

• Correcting TCM software or configuration where applicable

• Replacing the TCM when testing proves an internal module fault

Final Diagnosis

P0874 – Transmission Fluid Pressure Sensor/Switch "C" Circuit Intermittent means the transmission control system has detected an intermittent or unstable electrical condition associated with the Pressure Sensor/Switch "C" circuit.

The word "intermittent" should immediately make the technician think about wiring, connectors, terminal tension, heat, vibration, moisture, sensor behavior, and unstable power or ground.

At the same time, genuine hydraulic problems should not be dismissed.

The most reliable diagnostic strategy is to determine whether the problem is:

an intermittent electrical signal, an actual hydraulic pressure problem, or a combination of both.

Start with freeze-frame data and a complete module scan. Then inspect the connector and harness, verify power/reference/ground and signal integrity, monitor live data under the conditions that trigger the fault, and compare reported pressure with mechanically measured pressure when necessary.

Most importantly, do not replace the pressure sensor, valve body, transmission pump, or entire transmission simply because P0874 is stored. The code identifies where the control system detected an abnormality; proper testing determines which component actually needs repair.