P1128

MAP Sensor Signal Lower Than Expected

Car Fault Codes Honda Fuel & air

Can you still drive? With care, short trips only

Who can fix it? DIY with some experience

Typical repair time 20 minutes – 1.5 hours

Typical cost SAR 100 to 700

What it means

This is a Honda- and Acura-specific code; the same number can mean something different on other makes. The engine computer compared the manifold absolute pressure (MAP) reading with throttle opening and engine speed and found the pressure lower than it should be. It is similar in idea to generic P0106, and the cause is usually the sensor, its circuit or a wrong throttle reading.

Models covered: Honda and Acura models, mainly 1990s to early 2000s.

Symptoms4

Check engine light on.
Weak acceleration or hesitation.
Uneven idle in some cases.
Higher fuel use or reduced power.

Possible causes5

Faulty MAP sensor.
Dirty sensor port, or blocked hose on models that use one.
Corroded or loose sensor connector or wiring.
Faulty throttle position sensor (TPS) making the comparison wrong.
Engine computer fault (rare).

How to diagnose4

Compare the MAP reading with the engine off to atmospheric pressure, then at idle and under acceleration.
Watch the TPS reading while slowly pressing the pedal and confirm it changes smoothly.
Inspect the sensor port or hose for blockage or cracks.
Measure supply, signal and ground at the sensor against the manufacturer specification.

How to fix5

Clean the sensor port or replace the hose.
Repair the damaged connector or wire.
Replace the MAP sensor if its reading is wrong.
Fix the TPS if it is proven faulty.
Clear the code and confirm the readings make sense while driving.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for cleaning or a connector repair, and a little higher for a new MAP sensor or throttle position sensor.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

How does the computer know the MAP reading is too low?

It compares it with throttle opening and engine speed; if the throttle opens a lot and pressure stays low, the reading is not plausible.

Could the throttle position sensor be the cause?

Yes, since the comparison depends on it, so check the TPS along with the MAP sensor before replacing parts.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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