P1123 — Manifold Absolute Temperature Circuit Low Input

OBD2 code P1123 flags a problem with the sensor and actuator circuits (manifold absolute temperature circuit low input). The car is usually drivable while you plan the repair. Common culprits: corroded, loose or damaged connector, open or shorted wiring in the circuit, control module driver fault.

For Ford vehicles

throttle position sensor

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P1123 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the manifold absolute temperature for damage, corrosion, chafing or poor contact.
Subsystem check Check for supply voltage at the manifold absolute temperature connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P1123 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P1123 (parts and labor, USD, independent shop rates): Repair wiring or connectors: $80–$250; Replace the faulty sensor or actuator: $150–$500; Control module repair: $300–$1,000. Overall, fixing P1123 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How much does it cost to fix P1123?

Repair wiring or connectors — $80–$250; Replace the faulty sensor or actuator — $150–$500; Control module repair — $300–$1,000. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Is it safe to drive with P1123?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How do I diagnose P1123 myself?

Start with a scan: confirm P1123, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the manifold absolute temperature, and verify the suspect component against live data before buying parts.

What are the symptoms of P1123?

Drivers most often notice: Check Engine Light on, increased fuel consumption in some cases, the affected system operates intermittently or not at all, possible limp mode depending on the affected component.

What does OBD2 code P1123 mean?

When your scan tool displays P1123, the engine computer is flagging a voltage problem on the manifold absolute temperature circuit. Specifically, the signal has dropped below the minimum threshold the ECU expects to see — essentially sitting too close to ground potential. Technicians classify this as a "circuit low" condition, which places it squarely in the powertrain fault category affecting engine and transmission operation.

The manifold absolute temperature sensor (sometimes called the MAP sensor in other contexts) tracks intake manifold pressure and temperature to help the ECU calculate fuel delivery and ignition timing. When the voltage on its signal wire stays abnormally low, the computer can't make accurate measurements, so it sets P1123 and turns on the Check Engine light. The ECU typically needs to see this low-voltage condition persist across multiple drive cycles before it commits the code to memory, though some models set it on the first occurrence.

To pin down the problem, the engine control module compares real-time sensor data against factory-calibrated voltage windows. When readings fall outside those windows for the configured number of cycles, P1123 triggers and a freeze frame snapshot gets saved — capturing RPM, engine load, coolant temperature, and vehicle speed at the exact moment of failure. That snapshot becomes your starting point for diagnosis.

Common Symptoms of P1123

The Check Engine light illumination is the most obvious sign. Beyond that, you may notice:

Noticeably higher fuel consumption than usual
Intermittent operation or complete failure of the affected sensor system
Reduced engine performance or hesitation under load
Limp-home mode activation on some vehicles, limiting power output
Rough idle or unstable throttle response in certain configurations

What Triggers P1123?

The low voltage condition stems from several possible sources. Most often, you'll find one of these:

A broken or corroded wire creating an open circuit
The signal wire shorted directly to ground somewhere in the harness
Loss of the 5-volt reference voltage the sensor requires to operate
A failed manifold absolute temperature sensor dragging the circuit down
Loose or damaged connector pins allowing poor electrical contact
A blown fuse protecting the sensor circuit
Problems with the ground reference the sensor relies on
In rare cases, an internal fault within the ECU itself

Diagnosing P1123

Follow this structured approach to narrow down the cause without replacing parts unnecessarily.

Connect your OBD2 scanner and verify P1123 is stored. Record the freeze frame data before clearing anything — those conditions (RPM, load, temperature, speed) tell you exactly what to replicate during the retest.
Pull all stored codes from every module. Related codes on the same circuit often point directly to the failing component. Check for any outstanding TSBs (Technical Service Bulletins) for your specific make, model, and year — manufacturers sometimes release software updates or known-fix bulletins for common code patterns.
Perform a thorough visual inspection of the wiring harness and connectors tied to the manifold absolute temperature circuit. Look for cracked insulation, rubbed-through wires, corrosion buildup, or connectors that don't seat securely.
Check for 5-volt reference voltage at the sensor connector first. If that supply is missing, trace back to the ECU or main power feed. Then measure resistance from the signal wire to ground — a reading near zero ohms confirms a short-to-ground in the harness.
Test signal voltage, ground continuity, and reference voltage at the component side of the connector. Compare your readings against manufacturer specifications.
While monitoring live data on the scanner, gently wiggle the wiring harness and connectors. Any signal dropouts or wild fluctuations point to broken wires hidden inside the insulation.
Clear the code, complete a drive cycle that covers the freeze frame conditions (similar speed, load, and temperature), and verify P1123 does not return.

Repair Options and What to Expect

Address the cheapest probable causes before considering component replacement.

Wiring repair or connector replacement: $80–$250
Manifold absolute temperature sensor or actuator replacement: $150–$500
ECU or control module repair/reflashing: $300–$1,000

Most P1123 diagnoses reveal frayed wiring, corroded connectors, or a failed sensor as the culprit. Control module failures are uncommon but possible, so confirm all wiring and power supplies check out before suspecting the computer.

How Much Will Fixing P1123 Cost?

Your total bill depends entirely on which part has failed. Typical scenarios (parts and labor at independent shops, USD):

Wiring harness repair or connector replacement: $80–$250
Sensor or actuator replacement: $150–$500
Control module diagnosis and repair: $300–$1,000

Most shop visits land somewhere in the $150–$350 range once you've isolated the problem. Spending time on accurate diagnosis first almost always saves money compared to swapping expensive components on guesswork. The most extreme repair scenario (control module) rarely turns out to be the answer, but you won't know without checking the basics first.

Can You Drive with P1123?

The vehicle typically remains drivable even with P1123 stored. You may experience slightly reduced performance, elevated fuel consumption, or an inoperative auxiliary system depending on which circuit is affected. However, if the malfunction causes stalling, prevents starting, or triggers warnings related to braking or steering assist, treat it as an immediate safety concern and have it diagnosed right away.