Code
P1129
INFINITI
P — Powertrain
MAP Higher Than Expected
AI status
Completed
Completed
100%
Causes
- Faulty MAP sensor (out-of-spec output)
- Short or leakage in MAP sensor signal wiring (short to 5V)
- Poor sensor ground or bad reference 5V supply from PCM
- Intake system overpressure (wastegate stuck closed, turbo overboost)
- Blocked intake or restricted exhaust causing elevated intake pressure
- Vacuum/boost hose disconnected or leaking to pressurized source
Symptoms
- Check Engine Light / MIL illuminated
- Poor idle or rough running
- Hesitation, stumbling, or reduced power
- Higher than normal fuel consumption or black smoke (rich)
- Possible engine knock or ping under load
- Overboost conditions (in turbo engines) or limp mode
What to check
- Read freeze frame and pending codes; capture MAP, RPM, throttle position, ignition timing and fuel trim data with a scan tool
- Compare MAP sensor voltage and kPa reading to barometric pressure with key ON / engine OFF (should be ~ambient/BARO)
- Observe live MAP vs throttle: MAP should drop (lower kPa) at idle/high vacuum and rise with throttle/boost
- Backprobe MAP sensor connector: check reference voltage (~5.0 V), ground continuity, and signal voltage
- Inspect wiring and connector for damage, corrosion, pin pushed out, or moisture
- Unplug MAP sensor and verify PCM reaction (some vehicles set default value or trigger limp behavior)
Signal parameters
- Reference voltage (Vref): typically ~5.0 V from PCM (+/- 0.1–0.3 V depending on vehicle)
- Signal output: typical MAP sensors output ~0.5–4.5 V proportional to absolute pressure
- Key ON / Engine OFF: signal should approximate barometric pressure (~1 bar / ~100 kPa corresponding to about mid-scale voltage ~2.4–2.6 V)
- Idle (naturally aspirated): manifold pressure typically ~30–50 kPa (~0.5–1.5 V depending on sensor)
- Full boost (turbo): MAP can exceed atmospheric >100 kPa and signal approaches upper voltage (~3–4.5 V depending on calibration)
- Expect consistent, proportional changes in MAP voltage with throttle input and load
Diagnostic algorithm
- Retrieve and record freeze frame data and live MAP, BARO, RPM, TPS, MAF (if equipped), ignition timing and fuel trims.
- With key ON / engine OFF, record MAP signal voltage and compare to barometric pressure reading. If MAP signal is substantially higher than BARO, suspect sensor or wiring.
- Backprobe the MAP connector: verify Vref (~5 V), ground continuity to chassis/PCM, and measure signal voltage while varying throttle. Note any unusual/noisy signal.
- Wiggle test harness while monitoring signal for intermittent shorts/open circuits.
- Inspect sensor port and intake for contamination or obstruction; clean or clear as needed.
- Inspect vacuum/boost hoses and connections for leaks or misrouting. Check wastegate and boost control components on turbo engines for stuck/closed operation.
- If wiring and connectors check good, substitute a known-good MAP sensor or bench-test the suspect sensor to verify output vs pressure.
- If replacement sensor cures the code, retest and clear codes; road test to confirm. If symptoms persist with good sensor, perform PCM diagnostic and check for shorts to 5V or internal PCM fault.
- Document repairs and recheck freeze frame/live data to confirm normal MAP behavior and no reoccurrence of P1129.
Likely causes
- Failed MAP sensor
- Signal wire shorted to reference voltage
- Loose/poor ground at sensor or PCM
- Wastegate or boost control malfunction (if turbocharged)
- Intake/exhaust restriction producing higher than expected manifold pressure
Fault status
Status
MIL ON — ECM detected MAP sensor output higher than expected for conditions; fault stored. Investigate sensor, wiring, intake pressure control and PCM inputs.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email