P0879 — Transmission Fluid Pressure Sensor/Switch “D” Circuit Intermittent #

Note: The code label and wording may vary depending on the vehicle manufacturer.

• Transmission Fluid Pressure Sensor/Switch “D” Circuit Intermittent (Generic OBD-II)
• Transmission Fluid Pressure Switch “D” Intermittent Circuit (Chrysler/Jeep/Dodge/RAM)
• Transmission Oil Pressure Sensor/Switch “D” Circuit Intermittent (Honda/Acura)
• TFP Sensor D Circuit Intermittent (Ford/GM)

Summary of code P0879 #

The P0879 code indicates that the Transmission Fluid Pressure (TFP) Sensor/Switch “D” has experienced an intermittent electrical issue within its circuit. The TFP sensor monitors hydraulic pressure inside the automatic transmission, sending signals to the transmission control module (TCM) or powertrain control module (PCM). When the circuit signal becomes erratic or temporarily lost, the control system cannot reliably determine the true fluid pressure. This issue can cause erratic shifting, delayed engagement, or even damage to the transmission if not addressed. The code is commonly triggered by wiring faults, sensor degradation, or internal transmission issues.

Common symptoms for code P0879 #

A vehicle registering the P0879 code may display a variety of symptoms ranging from subtle to severe. Drivers should be alert to any unusual behavior in shifting or warning lights. Typical symptoms include:

• Check Engine Light or Transmission Warning Light illuminated
• Erratic or harsh shifting between gears
• Transmission slipping or failing to engage properly
• Delayed gear engagement, especially when starting from a stop
• Vehicle may enter “limp” or “fail-safe” mode, restricting performance
• Poor fuel economy due to improper gear selection
• Noticeable hesitation or surging during acceleration

Most probable causes for code P0879 #

The root causes for P0879 are most often electrical in nature, but can also arise from mechanical issues inside the transmission. Below is an ordered list of the most common causes, from most to least frequent:

1. Faulty Transmission Fluid Pressure Sensor/Switch “D” (internal sensor failure or contamination)
2. Loose, damaged, or corroded wiring/connectors in the TFP sensor “D” circuit
3. Intermittent grounding issues affecting sensor signal integrity
4. Low or contaminated transmission fluid, causing erratic hydraulic pressure readings
5. Internal transmission hydraulic problems (e.g., worn valve body or sticking pressure regulator)
6. Transmission control module (TCM) malfunction (rare, but possible)

Step-by-step diagnostic for code P0879 #

Diagnosing P0879 requires a methodical approach to avoid unnecessary part replacement. Always begin with the basics and work towards more complex possibilities:

1. Check transmission fluid level and quality. Top up or replace if low or dirty.
2. Inspect wiring and connectors at the TFP sensor “D” for damage, corrosion, or loose connection.
3. Clear the code and test drive to see if it returns (could be a temporary glitch).
4. Use a scan tool with live data to monitor TFP sensor readings under different driving conditions.
5. Perform a wiggle test on harness while observing live data for signal drops.
6. Check sensor reference voltage and ground with a digital multimeter.
7. If possible, bench-test or replace the TFP sensor “D” following OEM procedures.
8. If issue persists, inspect internal transmission components (consult a transmission specialist before opening the transmission).

Possible repairs for code P0879 #

Once the root cause is identified, repairs should target the specific fault. Here are the most common fixes linked to each cause:

• Replace faulty Transmission Fluid Pressure Sensor/Switch “D”
• Repair or replace damaged wiring/connectors in the sensor circuit
• Clean corroded connectors and ensure proper grounding
• Flush and refill transmission fluid with OEM-recommended type
• Address internal transmission issues (e.g., valve body cleaning/rebuild)
• Replace or reprogram the TCM if proven to be the root cause

Is it safe to drive with code P0879? #

Limited driving is possible, but not advisable. While the vehicle may still operate, driving with P0879 can quickly lead to further transmission damage due to unpredictable fluid pressures and shifting. If you notice harsh shifting, slipping, or the vehicle enters limp mode, stop driving and address the issue promptly to avoid costly repairs.

Vehicles most commonly affected by code P0879 #

P0879 is more frequently reported on certain makes and models, particularly those with advanced automatic transmissions using multiple pressure sensors. While it can occur on any OBD-II-equipped vehicle, it is most common on:

• Chrysler, Jeep, Dodge, and RAM vehicles (especially with 45RFE, 545RFE, 68RFE transmissions)
• Honda and Acura models (notably with the 5-speed automatic transmission)
• Ford vehicles using 6F35, 6R80, or similar transmissions
• GM vehicles with 6L80/6L90 or 4L60E transmissions

Common mistakes & best practices for P0879 #

When working with code P0879, technicians and DIYers often fall into a few traps. Here’s what to avoid, and what to do instead:

• Mistake: Replacing the TFP sensor without checking wiring or fluid condition.
• Mistake: Neglecting to clear the code and retest after any repair.
• Mistake: Ignoring the possibility of intermittent connector or ground faults.
• Best Practice: Always inspect wiring and connectors before replacing parts.
• Best Practice: Use live data to verify sensor operation and pinpoint intermittent faults.
• Best Practice: Consult OEM service information for exact sensor location, circuit logic, and test procedures.

Express FAQ for code P0879 #

Can a low transmission fluid level cause P0879?
Yes, low or contaminated fluid can cause erratic pressure readings, potentially triggering this code. Always check fluid level and quality first.

Is P0879 a sensor or transmission problem?
It can be either. Most often, it’s a sensor or wiring issue, but internal hydraulic problems in the transmission can also cause intermittent fluid pressure signals.

Will the code reset itself if I fix the problem?
Sometimes, but it’s always best to clear the code with a scan tool and confirm it does not return after repairs.

Do I need a special tool to diagnose P0879?
A scan tool capable of reading live transmission data, plus a basic digital multimeter, are highly recommended for accurate diagnosis.