Tech Stuff

Camry generations five and six: A brief tour of the Toyota Camry fuel and EVAP systems

Figure 1: Retainer clips are used on fuel pump module components.
<p>Figure 1: Retainer clips are used on fuel pump module components.</p>

Jacques Gordon has worked in the automotive industry for 40 years as a service technician, lab technician, trainer and technical writer. His began his writing career writing service manuals at Chilton Book Co. He currently holds ASE Master Technician and L1 certifications and has participated in ASE test writing workshops.

Since the day it was introduced to the U.S. market, the Toyota Camry has been one of the most reliable cars on the road. With normal maintenance or even a fair amount of neglect, it seems these cars almost never break down. When problems do arise, the diagnosis is rarely a challenge.

But diagnosis is always faster and more accurate when you know more about the vehicle. If you don’t normally work on Toyotas, or if you simply haven’t had the opportunity to look into a Toyota fuel system lately, here’s a quick overview of the two most common models.

The 2002-2006 model is the Camry’s fifth generation and the first year for the 2.4-liter 2AZ-FE engine with an electronic mass airflow sensor, electronic throttle and a returnless fuel injection system. That system architecture became the model for Toyota port fuel injected engines right up through current generation, including the other engines used in that car, the 3.0-liter 1MZ-FE and the 3.3-liter 3MZ-FE.

Returnless fuel systems were developed to reduce evaporative emissions. The main difference is the fuel pressure regulator is inside the fuel tank instead of under the hood. The fuel rail may have something that looks like a pressure regulator, but it’s actually a pulse damper to reduce pressure pulsation and fuel pump noise. The mechanical pressure regulator is part of the fuel pump module that includes the pump, a reservoir, the gauge sending unit and a fuel filter.

The fuel pump module is usually sold as a complete assembly, but according to the service manual each of those components can be replaced separately once the module is removed. That includes the only fuel filter in the whole system, the strainer or “sock” on the inlet side of the pump. Turbine pumps are not particularly strong on the suction side, so if there’s a no-start or driveability issue that’s caused by lack of fuel, the problem just might be nothing more than a clogged fuel filter.

Specs for this fuel system are the same for all three engines: fuel pressure with the engine running or not running is 44 to 50 psi, hold pressure is 21 psi and fuel injector resistance is 11.6 to 12.4 ohms at 68 degrees Fahrenheit (20 degrees Celsius).

There is no fuel pump flow rate specification, and there’s no pressure tap on the fuel rail either. One way to check fuel volume is to monitor fuel pressure during full-throttle acceleration. If fuel pressure falls below specification during a full-throttle acceleration, that means the fuel pump can’t keep up with the demand.

The fuel injection system’s electrical circuit design is the same on all three engines, but it is uniquely Toyota. Power for the fuel pump is supplied by what they call the circuit-opening relay (C/OPN), which any other manufacturer would simply call the fuel pump relay. Like other cars, power for the relay coil comes from the ignition switch (through a 10-amp fuse), and the ground circuit is provided by the PCM when the ignition switch is in the START position or when engine speed is above cranking speed.

What’s different here is that power for the C/OPN relay contacts is supplied by the main electronic fuel injection (EFI) relay, and power for this relay coil is provided by the PCM. Depending on the model, the EFI relay provides power to the fuel pump (through the C/OPN relay) the EVAP purge valve (VSV) and/or an oxygen sensor heater. This means you can’t really determine fuel pump voltage or current draw at the C/OPN relay socket, you’ll need to check it at the fuel pump connector itself. Fortunately that’s easily reached through the access panel under the rear seat.

By the way, Toyota OEM wiring diagrams are some of the most informative and user-friendly, and they often include notes about voltage, resistance and signal specs at the terminal connections.

Despite the Camry’s reputation for reliability, this was the first generation designed to meet LEV II evaporative emissions regulations. That means EVAP codes are common on these models because the EVAP system is relatively complicated: It includes the charcoal canister with a pressure sensor, two solenoid valves and some sophisticated software. The purge valve is under the hood, but the vent valve and pressure sensor are part of the canister assembly, and that’s mounted underneath right next to the fuel tank. This makes it easier to flood the canister if the tank is overfilled.

Figure 2: A fuel pump wiring diagram.
<p>Figure 2: A fuel pump wiring diagram.</p>

A complete and detailed service bay test is available in Toyota Service Bulletin EG048-04.

We’ll describe how the onboard EVAP monitors work here.

The PCM runs two different EVAP purge monitors to test the vacuum switching valve (VSV). That’s what Toyota calls the purge valve because it’s switched on and off in a duty cycle to control how much vacuum is applied to the canister. When the engine is running and all the normal drive-cycle criteria are met, the PCM turns on the canister closed valve (CCV), commonly called the vent valve. The CCV is normally open, so turning it on closes it. With the CCV closed, the PCM cycles the VSV and monitors the pressure sensor in the canister. If canister pressure doesn’t decrease during this test, the CCV is turned off (opened) and the PCM looks for a pressure increase of at least two inches of water (3.75 mmHg). If pressure still doesn’t change, the PCM decides the VSV is not opening and a pending code will be recorded in memory. If this happens on two consecutive trips, the PCM will illuminate the MIL and set code P0441 (purge flow incorrect).

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