Your 8th Gen (FA5/FG2), 9th Gen (FB6/FG4), or 10th Gen (FC1/FK7) Civic may display diagnostic trouble code P0108 — which indicates a high voltage condition in the manifold absolute pressure sensor circuit.
P0108 is defined as “MAP Sensor Circuit High Voltage”. This code indicates that the voltage signal from the MAP sensor is above the expected range — specifically 4.49V or approximately 160 kPa. On a Honda, the MAP sensor output typically ranges from 0.5V AT idle to approximately 4.5V at wide-open throttle. P0108 indicates the ECU is receiving a voltage that is outside the expected range.
This is a circuit fault, not a mechanical failure. It indicates the sensor’s electrical signal is shorted to voltage, the sensor has failed in the high direction, or there is a wiring issue. Before replacing components, perform electrical diagnostics using a digital multimeter (DMM). In most cases, this code is caused by a failed sensor, a short to 5V, or — on boosted vehicles — incorrect MAP sensor scaling in the tune.
The following is a technical breakdown of the typical causes of P0108 on these Honda Civic models and the recommended diagnostic and repair procedures.
P0108 Diagnostic Overview: High Voltage in MAP Circuit
P0108 (“MAP Sensor Circuit High Voltage”) is the counterpart to P0107. The ECU is not detecting a dead signal — it is detecting a signal that is pegged at high voltage.
On a properly functioning Honda, the 3-wire MAP sensor should output approximately 2.9V at KOEO (Key On, Engine Off) based on atmospheric pressure, and sweep from 0.5V at idle to 4.5V at WOT. The ECU stores P0108 when the MAP sensor voltage remains at 4.49V or higher for at least 2 seconds.
The MAP sensor circuit consists of three wires:
- Pin 1: 5V VCC reference from the ECU
- Pin 2: Signal wire back to the ECU
- Pin 3: Sensor ground
When the signal wire voltage exceeds 4.49V, the ECU stores P0108.
Primary Failure Modes for P0108
1. Failed Sensor (High Output)
Internal electronics can fail, sending a signal pegged at 5V. This is common on high-mileage R18, K-series, and L15B7 engines. Replacement is required.
2. Signal Wire Shorted to 5V Reference
The signal wire may chafe and contact the 5V reference wire. The ECU then reads a constant 5V on the signal line and stores P0108.
Test: Disconnect the MAP sensor. With KOEO, probe the signal wire (pin 2) with a DMM. If 5V is present on the signal wire with the sensor disconnected, the wire is shorted to the 5V reference in the harness. Trace and repair the wiring.
3. Open Signal Wire
If the signal wire is broken or disconnected, the voltage can float high. Honda’s diagnostic procedure for this: with the MAP disconnected, jump pins 2 and 3 (signal and ground). If the MAP reading in the data list drops, the wiring is functional — the sensor is the issue. If it remains high, there is an open in the signal wire.
4. Missing or Weak Sensor Ground
The MAP sensor requires a solid ground. If the ground wire (pin 3) is corroded or broken, the sensor output floats high.
Test: Disconnect the MAP. Check continuity between pin 3 on the harness side and chassis ground. If continuity is absent, locate and repair the break. Also check the engine ground strap — a poor main ground can cause sensor voltage issues.
5. Incorrect MAP Scaling in Tuning Software
On vehicles running Hondata FlashPro or KTuner with an aftermarket MAP sensor (3-bar, 4-bar, etc.), incorrect calibration scaling can cause false P0108 codes. The ECU expects a specific voltage curve — incorrect scaling results in high voltage readings.
Remedy: If using an e-tune from DRob (Innovative Motorworks) or Phearable, verify MAP sensor scaling matches the installed hardware.
Diagnostic Procedure — Factory Service Manual Flow
This diagnostic sequence is derived from Honda’s factory service manual.
Step 1: Check MAP Reading with a Scanner at KOEO.
With KOEO (Key On, Engine Off), monitor MAP sensor data. It should read approximately 101 kPa (2.9V). If it reads 160 kPa (4.49V) or higher, proceed to Step 2.
Step 2: Jump Terminals 2 and 3 (Signal and Ground).
Disconnect the MAP sensor. Use a jumper wire to connect pins 2 and 3 on the harness side. With KOEO, check the MAP reading on the scanner.
- If the reading drops to 0 kPa: The wiring is functional. The sensor is faulty. Replace it.
- If the reading remains high (160 kPa): The signal wire has an open circuit. Repair the wire between the MAP connector and the ECU.
Step 3: Verify 5V Reference.
Remove the jumper wire. Measure voltage between pins 1 and 3 on the harness side. Should be approximately 5V. If not, repair the 5V reference wire.
Step 4: If the 5V Reference is Correct and the Sensor Tests Bad.
Replace the MAP sensor. After replacement, perform an ECM/PCM reset and idle learn procedure.
The G101 Ground — A Common Issue on 8th/9th Gen
On 8th Gen (R18/K20Z3) and 9th Gen (K24Z7) Civics, the engine sensor ground circuit connects to the thermostat housing (labeled G101). If this ground connection becomes loose or corroded, the MAP ground (Pin 3) can float, causing P0108.
Remedy: Before replacing the sensor, disconnect the ground strap on the thermostat housing, clean the contact surfaces with a wire brush and brake cleaner, and reinstall securely. This is a no-cost repair that resolves many high-voltage codes.
Platform-Specific Considerations
8th Gen (FA5 / FG2 / R18 / K20Z3):
- K20Z3 (Si): With aftermarket intakes, check the harness near the intake tube. Tight installations can pull the MAP connector taut, causing intermittent shorts.
- R18 (Base): Check for harness chafing at the plastic injector cover edges.
- Check G101 ground on the thermostat housing — this is a common cause of P0108 on these vehicles.
9th Gen (FB6 / FG4 / K24Z7):
- If using an aftermarket tune, verify MAP sensor scaling is correct for the installed sensor.
- Check the G101 ground on the thermostat housing — corrosion here can cause the same issue as the 8th Gen.
10th & 11th Gen Turbo (FC1 / FK7 / FL1 / FL5 / L15B7 / K20C1):
- This platform uses both a MAP sensor on the manifold and a boost pressure sensor on the charge pipes.
- If running an aftermarket MAP sensor with an e-tune, ensure scaling is correctly configured.
- If a 3-bar or 4-bar MAP sensor was installed without updating the calibration, P0108 may be triggered.
- On the 1.5T, there are two sensors that can cause similar codes — the one on the manifold is the primary MAP.
- Ground locations differ from the 8th/9th Gen — check the main engine ground near the transmission and the ground on the cylinder head.
OEM Part Numbers
Verify fitment by VIN before ordering.
| Part | Fits | OEM Part Number | Approx. Cost |
|---|---|---|---|
| MAP Sensor | 2006–2011 Civic Si K20Z3, 8th Gen R18, 9th Gen K24Z7 | 37830-PNC-003 | $80–$150 (dealer) / $50–$100 (online) |
| MAP Sensor | 2016–2021 Civic 1.5T L15B7 | 37830-RPY-G12 | $60–$120 (dealer) |
| MAP Sensor | 2017–2021 Civic Type R K20C1 | Verify by VIN | $70–$130 |
Recommendation: Use OEM Honda or Denso sensors. Aftermarket sensors may have different voltage calibration curves, which can affect fuel trims and driveability.
Repair Cost Estimates
| Repair | DIY Cost | Independent Shop | Honda Dealer |
|---|---|---|---|
| MAP Sensor Replacement | $50–$150 (parts) | $180–$300 | $250–$400 |
| Wiring Repair (short to 5V) | $10–$50 (materials) | $100–$200 | $150–$300 |
| G101 Ground Cleaning (8th/9th Gen) | $0 (wire brush + brake cleaner) | $50–$100 | $100–$180 |
| Dealer Diagnostic Fee | N/A | N/A | $120–$200 |
Pricing based on current market rates from HondaPartsNow, RockAuto, and Majestic Honda.
Pre-Purchase Inspection Note
When evaluating a used Civic with a P0108 code, the seller may claim it is a vacuum leak or tuning issue. P0108 is an electrical fault, not a mechanical one. A relatively inexpensive sensor replacement would typically resolve the issue.
Recommendation: If the seller has not performed basic diagnostics or sensor replacement, it may indicate neglect of proper maintenance. Consider this in price negotiation.
Diagnostic Checklist
☐ P0108 = MAP Sensor Circuit High Voltage — signal above 4.49V
☐ Check MAP reading at KOEO — should be ~2.9V (101 kPa). 4.49V+ indicates a problem
☐ Test with jumper wire — disconnect MAP, jump pins 2 & 3. If MAP drops to 0 kPa, sensor is faulty. If it remains high, signal wire is open
☐ Check 5V reference — should be ~5V between pins 1 and 3. No voltage indicates an open in the reference wire
☐ Check signal wire for short to 5V — with sensor unplugged, probe pin 2. If 5V is present, signal wire is shorted to reference
☐ Check G101 ground on thermostat housing (8th/9th Gen) — clean and tighten. This is a common no-cost fix
☐ Check engine grounds — poor grounds can cause sensor voltage issues
☐ If running a tune, verify MAP scaling — aftermarket MAP sensors require correct scaling in the calibration
☐ Use OEM or Denso MAP sensors — aftermarket sensors may have incorrect voltage calibration curves
☐ If the code returns after sensor replacement and wiring inspection, suspect ECM — rare but possible
☐ Pre-purchase inspection: P0108 is an electrical fault, not mechanical — use this information when evaluating the vehicle