What Does P1121 Mean?
P1121 indicates the Throttle Position Sensor (TPS) signal is not consistent with the Mass Air Flow (MAF) sensor reading. The ECM has detected a disagreement between the throttle opening angle and the actual airflow entering the engine. This correlation fault means one of the two sensors is inaccurate, or there is an air leak allowing unmetered air past the MAF sensor. The engine may exhibit hesitation, surging, or poor throttle response.
Common Causes
30%
Vacuum leak between MAF sensor and intake manifold (unmetered air)
25%
Dirty or contaminated MAF sensor reading lower than actual airflow
20%
TPS sensor misadjusted or worn with inaccurate angle reporting
15%
Sticking or carbon-fouled throttle body not opening fully
10%
Intake manifold gasket leak allowing unmetered air
Diagnostic Steps
1
Step 1: Monitor both TPS percentage and MAF (g/s) simultaneously during a slow throttle sweep from idle to wide-open throttle. Both should increase proportionally — a disparity indicates the faulty sensor.
2
Step 2: Check for vacuum leaks using a smoke machine introduced into the intake. Focus on the area between the MAF sensor and the throttle body, as well as the intake manifold gaskets.
3
Step 3: Inspect and clean the throttle body. Carbon buildup can restrict airflow even when the TPS shows the throttle open, creating a disagreement between expected and actual airflow.
4
Step 4: Clean the MAF sensor element with MAF-specific cleaner. A contaminated sensor will undercount airflow, showing less air than the throttle position would predict.
5
Step 5: If the TPS is adjustable, verify proper voltage at closed throttle (typically 0.4–0.8V) and wide-open throttle (typically 4.0–4.5V). Adjust or replace if out of specification.
Estimated Repair Cost
$50 - $350
Parts + labor, varies by vehicle and location
P1121 indicates the Throttle Position Sensor (TPS) signal is not consistent with the Mass Air Flow (MAF) sensor reading. The ECM has detected a disagreement between the throttle opening angle and the actual airflow entering the engine. This correlation fault means one of the two sensors is inaccurat...
The most common cause of P1121 (Throttle Position Sensor Signal Not Consistent with Mass Airflow Signal) is: Vacuum leak between MAF sensor and intake manifold (unmetered air)
Typical repair costs for P1121 range from $50 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Inconsistent throttle and airflow data can cause unexpected surging or hesitation during acceleration. In electronic throttle control systems, the ECM may enter a reduced power mode as a safety measure, limiting vehicle speed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1121 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Management / Throttle and Air Metering
Difficulty
Type
Manufacturer
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