What Does P1112 Mean?
P1112 indicates either a dual alternator lower circuit malfunction or a MAP sensor circuit producing intermittent low voltage, depending on the manufacturer. This is the low-voltage counterpart to P1111. The MAP interpretation means the sensor signal sporadically drops below normal operating range, causing brief lean fuel corrections. The alternator interpretation points to a control circuit issue with the secondary charging unit.
Common Causes
30%
Intermittent open in the MAP sensor signal wire causing voltage dropouts
25%
MAP sensor ground connection intermittently failing
18%
Dual alternator lower unit control circuit open or shorted (if equipped)
17%
MAP sensor internally failing under thermal cycling
10%
5V reference circuit overloaded or unstable affecting MAP readings
Diagnostic Steps
1
Step 1: Monitor MAP sensor voltage over an extended period including warm-up. Record any voltage drops below the normal idle range of 1.0–2.0V that would indicate an intermittent fault.
2
Step 2: Perform a wiggle test on the MAP sensor connector, harness, and ECM connector while observing the MAP PID for dropouts.
3
Step 3: Measure voltage drop on the MAP sensor ground wire under operating conditions. High resistance grounds cause low signal voltage readings.
4
Step 4: Check the 5V reference circuit stability by backprobing the reference wire at the MAP sensor connector. If reference voltage fluctuates, check for other sensors on the shared circuit that may be pulling it down.
5
Step 5: For dual alternator applications: test the lower alternator control circuit for opens, shorts, and connector integrity. Verify the field circuit is receiving proper command signals.
Estimated Repair Cost
$50 - $400
Parts + labor, varies by vehicle and location
P1112 indicates either a dual alternator lower circuit malfunction or a MAP sensor circuit producing intermittent low voltage, depending on the manufacturer. This is the low-voltage counterpart to P1111. The MAP interpretation means the sensor signal sporadically drops below normal operating range, ...
The most common cause of P1112 (Dual Alternator Lower Circuit Malfunction/ Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent Low Voltage) is: Intermittent open in the MAP sensor signal wire causing voltage dropouts
Typical repair costs for P1112 range from $50 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Intermittent low MAP voltage can cause momentary lean misfires. While not immediately dangerous, repeated lean events can overheat catalytic converters and lead to potential fire risk in extreme cases.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1112 to identify the root cause.
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Powertrain
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Engine Management / Charging System
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