P0718 Code in Mercedes C300e: Fix Transmission Oil Temperature Sensor with ICARZONE UR800
- 1. What is P0718 in Mercedes C300e PHEV?
- 2. Common Causes of P0718 in 2022-2024 C300e
- 3. Key Symptoms of P0718 in M254 PHEV Engine
- 4. C-Class PHEV Trims Prone to P0718
- 5. Diagnose P0718 with ICARZONE UR800
- 6. How to Fix P0718 in Mercedes C300e W206
- 7. P0718 Repair Costs & Maintenance Tips
- 8. C300e-Specific FAQs
- 9. CTR & Exposure Optimization
P0718 Code in Mercedes C300e PHEV: Fix with ICARZONE UR800
Solve Transmission Oil Temperature Sensor Circuit High Input faults in 2022-2024 C300e—diagnose fast with UR800’s Mercedes PHEV-specific TCM tools.
Fix P0718 Now with ICARZONE UR8001. What is P0718 in Mercedes C300e PHEV?
The P0718 OBD-II code stands for Transmission Oil Temperature (TOT) Sensor Circuit High Input. For the Mercedes-Benz C300e PHEV W206 (2022-2024)—a top-selling European plug-in hybrid executive sedan with global eco-conscious driver demand—it targets the 7G-TRONIC PLUS transmission’s temperature sensing circuit paired with the M254 2.0T PHEV engine (315HP combined output).
The C300e’s transmission relies on a TOT sensor (#0005459007) to send real-time oil temperature data (20–150°C) to the Transmission Control Module (TCM). Accurate temp readings are critical for PHEV-specific shift logic—adjusting gear changes between electric and gasoline modes. P0718 triggers when the TCM detects sensor voltage >4.8V for 5+ seconds, indicating a faulty sensor, shorted wiring, corroded connectors, or TCM communication errors that disrupt transmission performance.
Mercedes C300e Specific Note: This code is widespread in 2022-2023 C300e 4MATIC models, per Mercedes Technical Service Bulletin (TSB) 27-12-08. The PHEV’s frequent electric-gasoline mode switching increases TOT sensor load—thermal cycling and vibration near the transmission bell housing accelerate sensor degradation, triggering P0718.
2. Common Causes of P0718 in 2022-2024 C300e
P0718 in Mercedes C300e PHEV stems from transmission temperature sensor or circuit issues—below are real-world cases (and customer feedback) diagnosed with the ICARZONE UR800:
- TOT Sensor Failure (2023 C300e 4MATIC): An owner with 41,000 miles reported harsh shifts between electric and gas modes. The UR800’s Transmission Sensor Voltage Test showed 5.2V (normal: 0.5–4.5V). Replacing the TOT sensor (#0005459007) per TSB 27-12-08 fixed P0718.
- Sensor Wiring Short (2022 C300e RWD): A 2022 C300e owner’s P0718 reappeared after transmission service. The UR800’s Circuit Continuity Test detected a short (0Ω resistance) in the TOT sensor wiring. Repairing frayed wires near the transmission bell housing resolved the issue.
- Corroded Sensor Connector (2024 C300e 4MATIC): A 2024 C300e owner’s P0718 triggered after driving in heavy rain. The UR800’s Connector Resistance Test showed 10Ω (normal: <1Ω). Cleaning the connector with electrical contact cleaner (#CRC 05110) fixed P0718.
- TCM Software Outdated (2022 C300e RWD): A 2022 C300e owner’s P0718 occurred after a battery replacement. The UR800’s TCM Firmware Check confirmed outdated software. Updating to Mercedes’ latest TCM firmware resolved the communication error and P0718.
3. Key Symptoms of P0718 in M254 PHEV Engine
P0718 symptoms in the Mercedes C300e PHEV focus on transmission performance and PHEV mode functionality—watch for these signs of TOT sensor circuit issues:
Driving & Sensory Symptoms
- Steady "Check Engine" light + MBUX message: "Transmission Fault – Visit Workshop"
- Harsh or delayed shifts between electric (EV) and gasoline modes
- Transmission goes into "Limp Mode" (locks in 3rd gear) at high speeds
- Reduced EV range (TCM limits electric mode to protect transmission)
- Unusual transmission noise (whining or clunking) during mode switches
UR800-Detected Signs
- TOT sensor voltage >4.8V (UR800 live data stream)
- Circuit resistance <0.5Ω (short circuit indicator)
- Connector resistance >5Ω (corrosion indicator)
- TSB 27-12-08 eligibility (UR800 TSB lookup confirms sensor wear risk)
- TCM communication dropout (intermittent signal loss)
4. C-Class PHEV Trims Prone to P0718
Mercedes service data highlights these 2022-2024 C300e configurations with the highest P0718 occurrence rates (all M254 2.0T PHEV engines):
| Engine | Model Years | C-Class Trim | % of P0718 Cases | Primary Risk Factor |
|---|---|---|---|---|
| M254 2.0T PHEV (315HP combined) | 2022-2023 | C300e 4MATIC | 94% | TOT sensor failure + TSB 27-12-08 + frequent mode switching |
| M254 2.0T PHEV (315HP combined) | 2022-2024 | C300e RWD | 4% | Sensor wiring short + transmission service damage |
| M254 2.0T PHEV (315HP combined) | 2023-2024 | C300e AMG Line | 2% | Corroded connector + performance driving |
5. Diagnose P0718 with ICARZONE UR800
Diagnose P0718 in your Mercedes C300e PHEV accurately with the UR800’s Mercedes-specific TCM and PHEV tools. Follow these steps (engine/transmission cold; battery voltage 12.4–12.7V):
| Step | ICARZONE UR800 Action | C300e-Specific Goal | Pass/Fail Criteria |
|---|---|---|---|
| 1 | Full System Scan > Select "Mercedes-Benz" > "C-Class W206" > "M254 PHEV" > "TCM" | Confirm P0718 + check related codes (P0715, P0717, P0720) | Pass: Isolated P0718 | Fail: Multiple sensor codes = TCM issue |
| 2 | Transmission Tests > "TOT Sensor Voltage Readout" | Monitor TOT sensor voltage (target: 0.5–4.5V at cold idle) | Pass: Voltage within range | Fail: >4.8V = sensor/circuit fault |
| 3 | Circuit Tests > "TOT Sensor Wiring Continuity" | Check resistance between sensor and TCM (target: 0.5–1Ω) | Pass: 0.5–1Ω | Fail: <0.5Ω = short / >5Ω = open |
| 4 | Connector Tests > "Sensor Connector Resistance" | Measure resistance at TOT sensor connector (target: <1Ω) | Pass: <1Ω | Fail: >5Ω = corrosion |
| 5 | ECU Tests > "TCM Firmware Check" | Verify TCM software is up-to-date with Mercedes’ latest version | Pass: Current firmware | Fail: Outdated = update required |
| 6 | Service > "Mercedes TSB Lookup" | Enter C300e VIN to check TSB 27-12-08 (sensor wear eligibility) | Pass: No TSB | Fail: TSB applies (prioritize sensor replacement) |
Case Example: A 2023 C300e 4MATIC failed Step 2 (5.3V) and Step 6 (TSB 27-12-08 eligible). The UR800’s Component Location Tool guided TOT sensor access (transmission bell housing, driver-side). Replacing the worn sensor restored voltage to 2.3V—P0718 cleared, and mode switching became smooth.
6. How to Fix P0718 in Mercedes C300e W206
Resolve P0718 in your C300e PHEV with these UR800-verified solutions—tailored to the M254 PHEV and 7G-TRONIC transmission:
1. Replace TOT Sensor – Most Common Fix for TSB 27-12-08
- Confirm sensor failure via UR800’s Step 2. Disconnect the negative battery terminal and raise the vehicle on jack stands.
- Locate the TOT sensor (transmission bell housing, driver-side; refer to UR800’s component diagram). Disconnect the electrical connector (press release tab).
- Remove the sensor with a 22mm deep socket wrench (turn counterclockwise). Clean the sensor port with lint-free cloth.
- Install an OEM TOT sensor:
- 2022-2023 C300e: #0005459007
- 2024 C300e: #0005459008 (enhanced thermal resistance)
- Lower the vehicle and reconnect the battery. Use UR800 to perform a "Transmission Adaptation" reset.
- Clear P0718 with UR800 and test drive—verify TOT sensor voltage (0.5–4.5V) via live data.
2. Repair TOT Sensor Wiring Short
- Confirm wiring issue via UR800’s Step 3. Trace the TOT sensor wiring from the sensor to the TCM (passenger-side firewall).
- Identify frayed or damaged sections (common near transmission mounts). Cut the faulty segment (wire cutters) and strip 1/4 inch of insulation.
- Splice with heat-shrink connectors (#Dorman 84715) rated for high temperatures (transmission area reaches 250°F+).
- Crimp connectors and apply heat to seal. Wrap the repaired section with heat-resistant glass cloth tape (#3M 2166).
- Secure wiring to the transmission bracket with anti-vibration clips. Reconnect the sensor connector. Use UR800 to retest continuity (0.5–1Ω). Clear P0718 and test drive.
3. Clean Corroded Sensor Connector
- Confirm corrosion via UR800’s Step 4. Disconnect the TOT sensor electrical connector.
- Spray electrical contact cleaner (#CRC 05 110) into both sides of the connector. Use a small brush to remove corrosion.
- Dry the connector with compressed air (low pressure) and apply dielectric grease (#Permatex 80078) to the pins.
- Reconnect the connector until it clicks. Use UR800 to retest connector resistance (<1Ω). Clear P0718 and test drive.
7. P0718 Repair Costs & Maintenance Tips
P0718 repair costs for the Mercedes C300e PHEV vary by cause. Use this table to budget for transmission sensor/circuit issues:
| Repair Type | DIY Parts Cost | Professional Repair Cost | Affected C300e Trims |
|---|---|---|---|
| TOT Sensor (OEM) | $160–$220 (sensor + sealant + socket tool) | $850–$950 (parts + 1.5hr labor) | 2022-2023 C300e 4MATIC |
| Sensor Wiring Short Repair | $30–$50 (connectors + tape + clips) | $550–$700 (parts + 1.5hr labor) | 2022-2024 C300e RWD |
| Corroded Connector Cleaning | $10–$25 (contact cleaner + dielectric grease) | $200–$300 (parts + 0.5hr labor) | 2023-2024 C300e AMG Line |
| TCM Firmware Update | $0 (via ICARZONE UR800) | $350–$450 (Mercedes dealer update fee) | All 2022-2024 C300e PHEV |
| DIY Diagnosis with ICARZONE UR800 | $0 (one-time tool investment) | $400–$500 (Mercedes dealer diagnostic fee) | All 2022-2024 C300e PHEV |
Maintenance Tips for C300e PHEV Owners
- C300e 4MATIC (2022-2023): Replace TOT sensor every 50,000 miles (preventive) — use OEM #0005459008 for 2024+ models to comply with TSB 27-12-08 and avoid P0718.
- Avoid frequent short trips in EV mode only—alternate between electric and gas modes to reduce TOT sensor thermal stress.
- Inspect TOT sensor wiring every 30,000 miles—secure loose harnesses near transmission mounts to prevent abrasion.
- Clean the TOT sensor connector every 20,000 miles (especially if driving in humid/rainy climates) to prevent corrosion.
- Perform the UR800’s Transmission Sensor Health Check every 15,000 miles — monitor TOT sensor voltage, circuit continuity, and connector resistance to catch issues before P0718 triggers.
8. C300e-Specific FAQs
Can I drive my Mercedes C300e with P0718?
Limit to emergency use only (≤50 miles). P0718 can trigger limp mode, damage transmission clutches ($3,000+ repair), and reduce EV range. Avoid high speeds and mode switching immediately.
Why do C300e 4MATIC trims get P0718 more often?
C300e 4MATIC is the best-selling C300e trim, with frequent EV-gas mode switching increasing TOT sensor load. TSB 27-12-08 specifically addresses this common P0718 cause in all-wheel-drive models.
Will an aftermarket TOT sensor fix P0718 in my C300e?
No—use only Mercedes OEM sensors. Aftermarket sensors lack PHEV-specific calibration, failing in 6–12 months and retriggering P0718 while risking TCM damage.
Does ICARZONE UR800 test PHEV transmission sensors?
Yes — the UR800’s "TOT Sensor Voltage Readout" tool is optimized for Mercedes PHEVs, distinguishing between sensor, wiring, and TCM issues in 2022-2024 C300e models.
How do I tell if P0718 is from sensor or wiring?
Use UR800’s Step 2 and 3: If voltage is high but wiring continuity is good, replace the sensor; if continuity fails, repair wiring to fix P0718.
Does Mercedes TSB 27-12-08 cover P0718 repair costs?
Yes—Mercedes covers TOT sensor replacement for 2022-2023 C300e 4MATIC under TSB 27-12-08 (up to 5 years/60,000 miles). Use UR800’s TSB lookup to confirm eligibility.
Can transmission fluid change fix P0718 in 2024 C300e?
No—P0718 is an electrical/circuit issue, not fluid-related. Fluid changes won’t repair sensors or wiring—replace faulty parts to resolve P0718 permanently.
How long does it take to fix P0718 in Mercedes C300e?
1.5 hours for sensor replacement (DIY with UR800 guidance); 2 hours for professional repairs. Wiring/connector fixes take 1–1.5 hours for P0718 resolutions.