RMW Code 34

On the way home from dinner tonight while waiting at a light, the head lights dimmed momentarily, then the CEL came on. It went out few seconds later. I checked the through the climate control and got a code 34 "MAP sensor signal voltage was too low (high vacuum) when engine speed was under 700 RPM, or when TPS was greater than 20% with an engine speed above 700 RPM"

Could that have had anything to do with my headlights dimming for some reason? The car runs perfectly.

So far you have an incident. If it happens again, then it becomes an intermittant problem and you have something to worry about.

CODE 34

Trouble Code 34 indicates that the Mass Air Flow (MAF) sensor is reporting less air is entering the engine than makes sense based on RPM and TPS. The MAF sensor produces a frequency output; around 30 Hz at idle to 150 Hz under acceleration. The frequency varies proportionally to airflow. The ECM monitors the frequency and thus determines airflow into the engine. Typical idle MAF is 5 to 7 grams per second.

The conditions for setting this code are:

* no Code 21 or 22 (TPS Error) present, and
* the air flow reported is < 4 grams per second, and
* TPS indicates 10% or more throttle position, and
* the engine speed is 1800 RPM or higher, and
* the above conditions exist for over 5 seconds.


Typical causes for this code include:

1) Faulty air ducting to or from MAF sensor
2) Faulty ECM-to-MAF connections
3) Poor routing of MAF harness (i.e. near coil packs)
4) Maladjusted TPS sensor
5) Defective MAF sensor
6) Defective ECM

[You must be registered and logged in to see this link.]

I realize this post is a month old, but I need to correct the diagnoses.
Though a Code 34 in the 80’s was MAF code in the 90’s it became a MAP code.

DTC 34
Manifold Absolute Pressure (MAP) Sensor Circuit
(Signal Voltage Low - High Vacuum)

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure(MAP) sensor responds to changes in manifold pressure (vacuum). The Powertrain Control Module (PCM) receives this information as a signal voltage that will vary from about 1.0 - 1.5 volts at idle to 4.0 - 4.8 volts at Wide Open Throttle(WOT) .

The scan tool displays manifold pressure in kPa of pressure and voltage Low pressure (high vacuum) indicates a low voltage while a high pressure (low vacuum) indicates a high voltage.

DIAGNOSTIC TROUBLE CODE (DTC) 34 WILL SET WHEN
MAP is less than 16 kPa, and RPM is less than 700 RPM, DTC 21 not set or MAP less than 20 kPa, RPM greater than 700 RPM, TP sensor angle greater than 26% and DTC 21 not set.

If you have a scaner, the test it. Otherwise, I would just buy a new one and be done with it.
--Robert

As far as I know my scan tool doesn't show the actual pressure, just the voltage the sensor is putting out. The problem is so random its hard to catch it with the scan tool to see what kind of voltage it has.