P1129

MAP Sensor Signal Higher 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 80 to 700

What it means

This is a Honda- and Acura-specific code; the same number can mean something different on other makes. The manifold absolute pressure (MAP) reading is higher than the engine computer expects for the throttle opening and engine speed, meaning intake vacuum looks weaker than it should. Common causes are an air leak into the manifold or a faulty sensor.

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

Symptoms4

Check engine light on.
High or uneven idle.
Hissing or sucking noise from the engine bay if there is a leak.
Higher fuel use or weaker performance.

Possible causes6

Vacuum leak from hoses or the intake manifold gasket.
Faulty MAP sensor.
Cracked or disconnected sensor hose on models that use one.
Signal wire shorted to voltage, or a poor ground.
Faulty throttle position sensor (TPS) making the comparison wrong.
Weak combustion or low cylinder compression reducing vacuum.

How to diagnose5

Compare the MAP reading with the engine off to atmospheric pressure; a higher reading points to the sensor or its circuit.
Watch the MAP reading at idle; a high reading with a lean mixture points to a vacuum leak.
Have a smoke test done on the intake manifold and hoses.
Check signal voltage and ground at the sensor against the manufacturer specification.
If misfire codes are also stored, check cylinder compression.

How to fix5

Replace the leaking vacuum hose or gasket.
Repair the ground or the shorted wire.
Replace the MAP sensor if it reads wrong with the engine off.
Fix the TPS if it is proven faulty.
Clear the code and confirm the idle reading returns to normal.

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.

A vacuum hose is a cheap fix; the cost rises a little for a new sensor or an intake manifold gasket.

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

Can a vacuum leak cause P1129?

Yes. A leak raises manifold pressure so the sensor reads higher than expected, which is why the check starts with the vacuum hoses.

How do I tell a bad sensor from a vacuum leak?

If the reading is wrong with the engine off, the sensor or its circuit is at fault; if it is right and then high at idle, a leak is more likely.

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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