Fault Code 13


Description:  MAP (Manifold Absolute Pressure) sensor pneumatic failure: sensor output does not change
Power loss light:  On
Limp-in mode:  TPS and engine speed used as an indication of manifold pressure

Possible Causes

Broken or disconnected vaccum line - Check the vaccum line leading from the MAP sensor.  On '87 and later engines, the sensor is located on the right shock tower and the vaccum line often gets pulled or pushed off.  Replace the entire line with a piece of 1/8" I.D. vaccum hose making sure to provide enough slack in the line.

Bad Baro-read solenoid - The barometric read solenoid may not be operating.  Try bypassing the solenoid, connecting the MAP sensor directly to the manifold to see if the engine runs better (this may not prevent the code 13, however).  If not accompanied by a code 37, you can try to repair or replace the solenoid.  See the Understanding Solenoids page for information about how to test and repair solenoids.

Moisture in MAP sensor - If this mostly occurs old cold weather, then you may have water that is freezing inside the sensor.  This is a common problem on vehicles that have the sensor located on the logic module.  Remove the sensor and bring inside to warm up.  Shake any droplets out of the sensor and set it in a warm, dry place for a day or so.  Don't try to take the sensor apart because you may destroy it.  Check all your vaccum lines because a vaccum leak would be the most likely cause of water entering the system.  If your MAP sensor is located on or near the logic module, you may wish to consider moving it under the hood on the right shock tower.  All 1987 and later models were set up this way to prevent moisture collection in the MAP sensor.

Pinhole leak in Fuel Pressure Regulator - Occasionally, a small leak will develop in the fuel pressure regulator diaphram that allows fuel to enter the vacuum system.  This upsets the response of the vacuum system, triggering this code.  Check for the presence of fuel in the vacuum line to the fuel pressure regulator.  If fuel is present, replace the regulator.

MAP sensor failure - A bad MAP sensor will usually cause a code 14, so this is not as likely to be the cause of a code 13.  But if it comes down to it, replace the MAP sensor which is located on the right shock tower on '87 and later vehicles or in the logic module on previous vehicles.  Damage from freezing water can destroy a MAP sensor.

Diagnostic Method

Trigger Parameters

- Just as the engine starts running (after cranking)
- MAP sensor output voltage does not change by more than 0.04V

Results If Component Fails

A fault code 13 is stored, the power loss light is turned on, and the system will enter limp-in mode.  The AIS will then be completely closed and the logic module will use the TPS and the ignition reference sensor to guess what the manifold pressure is.  Also, the engine speed will be limited to 2,000 rpm on turbo engines when the throttle plate is opened more than 22 degrees to prevent overboost.

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Updated 11/07/2003.

Copyright © 1996-2003 Russ W. Knize.