P077C GMC Code - Transmission Output Speed Sensor Circuit Low Voltage
Quick Answer
The Output Speed Sensor (OSS) is a hall-effect type sensor. Common causes include Faulty Transmission Output Speed Sensor (OSS), Transmission Output Speed Sensor harness is open or shorted, Transmission Output Speed Sensor circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P077C GMC indicates Transmission Output Speed Sensor Circuit Low Voltage.
- Common causes
- Common causes include Faulty Transmission Output Speed Sensor (OSS), Transmission Output Speed Sensor harness is open or shorted, Transmission Output Speed Sensor circuit poor electrical connection.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code P077C GMC Description
The Diagnostic Trouble Code (DTC) will be set when the TCM detects the vehicle speed sensor signal circuit voltage is less than 0.25 V for 0.8 s.
What are the Possible Causes of the DTC P077C GMC?
- Faulty Transmission Output Speed Sensor (OSS)
- Transmission Output Speed Sensor harness is open or shorted
- Transmission Output Speed Sensor circuit poor electrical connection
- Faulty Transmission Control Module (TCM)
How to Fix the DTC P077C GMC?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P077C GMC code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
Need more information about the P077C GMC code?
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Need Help with the Code?
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Information for Specific GMC Models
- P077C 2014 GMC Sierra — Transmission Output Speed Sensor Circuit Low Voltage
- P077C 2015 GMC Sierra — Transmission Output Speed Sensor Circuit Low Voltage
- P077C 2016 GMC Sierra — Transmission Output Speed Sensor Circuit Low Voltage
- P077C 2017 GMC Sierra — Transmission Output Speed Sensor Circuit Low Voltage
- P077C 2018 GMC Sierra — Transmission Output Speed Sensor Circuit Low Voltage
Frequently Asked Questions about P077C GMC Code
1. What does the OBDII code P077C mean for a GMC vehicle?
P077C indicates a low voltage issue in the transmission output speed sensor circuit, which monitors the rotational speed of the transmission output shaft.
2. What are the common symptoms of code P077C in a GMC?
Symptoms may include erratic shifting, transmission slipping, reduced fuel efficiency, a lit check engine light, or the transmission entering limp mode.
3. What causes the P077C code to appear?
The code can be triggered by a faulty output speed sensor, damaged wiring or connectors in the circuit, low transmission fluid, or an issue with the powertrain control module (PCM).
4. Can driving with the P077C code damage my GMC's transmission?
Yes, continued driving with this code can lead to further transmission issues or damage due to improper shifting or slipping.
5. How do I diagnose the P077C code on my GMC?
Start by inspecting the wiring and connectors for damage or corrosion, check the output speed sensor for proper operation, and ensure the transmission fluid level is correct.
6. How do I fix the P077C code in a GMC vehicle?
Repairs may involve replacing the output speed sensor, repairing or replacing damaged wiring, cleaning corroded connectors, or reprogramming the PCM if necessary.
7. How much does it cost to fix a P077C code on a GMC?
Costs vary depending on the issue. Replacing an output speed sensor typically costs $100–$300, while addressing wiring or PCM issues may cost more.
8. Can low transmission fluid cause the P077C code in a GMC?
Yes, low or contaminated transmission fluid can interfere with sensor operation and trigger this code.
9. Is the P077C code specific to GMC vehicles?
No, while it can appear in GMC vehicles, the P077C code is a generic OBDII code and may also occur in other makes and models.
10. Do I need professional help to repair the P077C code on my GMC?
If you're comfortable inspecting wiring and replacing sensors, you may be able to fix it yourself. Otherwise, seek help from a qualified mechanic.
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