MACS Monthly Newsletter - 2017 - APR7

Shops seem to have heard that Denso compressors in a range diagnostic link connector ("DLC3") and using the data list for air
of Toyota products have something called a flow sensor, and conditioning from the body electrical menu. If you don't have
we've been asked to comment and explain.
a Techstream (basically a dealer scantool), you can get a TechThe subject came up because when the sensor fails, techni- stream Lite kit, which allows your PC to run the factory softcians have reported, the air conditioning performance fails - ware . The "Lite" features the Drew Technologies "Mongoose
warm air from the HVAC vents. They've discovered that this Pro Toyota 2," which you can buy from the manufacturer or in
sensor is involved because there's a trouble code-No. B1479 a full kit from Toyota dealers. Yes, it gives you the capability to
and the service information says it's in the flow sensor circuit. reprogram, so here's "another broken record" recommendation
The code may be stored as an active one or a history code.
from MACS Service Reports.
There apparently were some issues with the A/C compressor
The B1479 code, as noted, is the definitive word for the flow
on a number of Toyota products, particularly the 2012-13 Camry sensor circuit, and if you don't have that code, the problem with
with the 2AR-FE-that's the 2.5-liter in-line four-cylinder; and the A/C is elsewhere. The diagnostic sequence with the "Lite"
the 2GR-FE, which is the 3.5-liter 60-degree V6. And both those is in a service bulletin, and we always assume that you have acengines have that compressor with the flow sensor (as do other cess to bulletins, and rarely repeat material from them in these
Toyota products, including the Prius). The important thing to pages.
note is that the sensor is not available as a detail part, so if it's
Toyota also includes a harness test that requires nothing more
bad, the only fix is to replace the compressor, on which the sen- than an ohmmeter (remember, the B1479 code is a circuit code,
sor is mounted.
not a parts failure code). The harness test is made at the A/C
Now let's take a look at this sensor and its circuit.
amplifier with the sensor wiring unplugged, and the procedure
The sensor is engineered to determine the amount of refrig- is to look either for low resistance ("below 1 ohm", although it
erant flow into the compressor, converting the flow to a volt- shouldn't be surprising to get readings slightly higher) or 10,000
age that varies inversely and proportionally, and that voltage is ohm or higher. Once again, the details are in a service bulletin. ■
transmitted to the A/C amplifier.
As the flow increases, the voltage drops;
as the flow drops, the voltage increases. It's
a five-volt circuit, with the reference voltage
supplied by the amplifier, which produces a
proportional signal to the engine control module (ECM) through the CAN bus (Controller
Area Network). The ECM uses that signal to
control engine r.p.m. while the A/C is on. If
the system has an electric motor-driven compressor, the r.p.m. of the compressor (as with
a Prius or other hybrids) is increased or decreased as indicated. So the sensor readings
serve to "tune" the compressor output to the
cooling needs of the system.
How the sensor works: it's basically a mass
flow device that uses a spool that moves according to the amount of refrigerant flow
(FIG. 11). There is a magnet on the spool, and
the spool movement changes the magnetic
flux, which changes the output voltage from
the sensor.
That sensor should output a fluctuating
0.7 to 3.8 volts with the blower switch on high
and the system running. With the A/C and
blower off, and ignition on, the voltage should
be 3.8-4.2 volts. If the voltage is constant (0.7
to 4.2 V) for more than four seconds with the
system turned on, that confirms the sensor is
Figure 11: Flow sensor on many Denso compressors is an efficiency tuning device that changes
defective.
engine r.p.m or compressor speed according to refrigerant flow. But if sensor fails, it is not availThe voltage measurements are per the Toyable as a detail part-entire compressor must be changed. Sensor operates a spool valve that
ota Techstream, connected to that underdash
changes flux of magnet, which provides output signal to A/C amplifier.

April 2017

MACS Service Reports

techinfo.toyota.com

THE NEW DENSO COMPRESSORS - DISCUSSION BY POPULAR REQUEST

http://www.techinfo.toyota.com

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2017