AfterMarketNews Auto Care Pro AutoProJobs Auto-Video.com Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service

Automotive Pet Peeves 2: Reader Feedback Is Overwhelming

How many auto repair pet peeves are out there? Well, enough of them that one article wouldn’t hold them all. I’ve received so many emails, texts and phone calls about my article in the February issue that I thought: why not put everyone’s pet peeve...

Read more...

Air Filter Show & Tell: Seeing Is Believing

Air filters are normal wear items that ­require regular checks and ­replacement. Their role is to trap dirt particles that can cause damage to engine cylinders, walls, pistons and piston rings. In fuel-injected vehicles, the air filter also plays...

Read more...

Searching For 'Black Holes': Job Totals Reveal Missed Selling Opportunities

The concept for Maintenance Chronicle is simple: We ask one shop to record their maintenance sales for a two-week period, and then we see what we learn from the results. This edition of Maintenance Chronicle also proved to be valuable for the shop we...

Read more...

Saab: Fuel Sending Unit Replacement

The 2006 Saab 9-3 Sport sedan came in on the hook and the tow truck driver said, “I think it needs a fuel pump.” The gas gauge was reading less than a quarter of a tank and the low fuel warning light wasn’t on, so a quick fuel pressure check was...

Read more...

KIA: Brake Light On, Tachometer And Speedometer Inoperative

Applicable Models: 2001 Kia Optima LX, 2.4L Complaint The customer states the red brake light is illuminated on the instrument cluster. The ­customer also states the tachometer and speedometer intermittently stop working. Cause Confirmed the customer’s...

Read more...

Mazda: Fuel System Servicing Precaution

Applicable Models: 2004-’07 Mazda3 2005-’07 Mazda6 2006-’07 MX-5 vehicles During service/removal of fuel system parts on the above vehicles, the memory of the malfunctions and the long-term fuel trim need to be cleared by either removing the...

Read more...

Ford: ABS Light On With DTCs C1175, C1236, P0500 or P0503

Model: 2005-’07 Super Duty Some 2005-‘07 Ford Super Duty vehicles may exhibit an ABS light on and possible diagnostic trouble codes (DTCs) C1175, C1236, P0500 and/or P0503. This condition may be due to faulty vehicle wiring, a failed wheel speed...

Read more...

Composite Rotors Are Back

Veteran technicians will remember the problems with composite rotors in the late 1990s. These rotors had hats of stamped steel cast into the iron rotor. They saved weight, but they were prone to runout and installation errors. These types of rotors...

Read more...

Power Steering Dynamics and Diagnostics

Twenty-five years ago, when the power steering failed, diagnosing the system was easy. The most difficult problem to diagnose was the “morning sickness” that plagued some ­vehicles when they were cold. Today, the introduction of speed sensitive steering,...

Read more...

Top 5 Tools: Daniel Sjobeck, Roseville Auto Repair

Daniel Sjobeck, tech Roseville Auto Repair Roseville, MN A good toolbox. You can have the best of everything, but it’s no use if you cannot find it. Power Probe – One of the greatest ­inventions EVER. Snap-on Digital Torque Wrenches Snap-on...

Read more...

Mitchell 1 ProDemand Consolidates Vintage Repair and Estimating Information

Mitchell 1 has updated its ProDemand repair, diagnostic and maintenance software by consolidating vintage repair and estimating information into the application to deliver full year, make and model coverage from 1974 to the present year. This latest enhancement...

Read more...

Pulling Codes: Multiple Misfire Personalities

A Story of Codes P0302, 04, 06, 08 & 03   This month’s diagnostic journey begins with a 2008 Land Rover Discovery that is taken in to a local testing facility for an emission test and fails due to a series of misfire codes. Misfire...

Read more...

Home Emissions Pulling Codes: The Story of Code P0456

Print Print Email Email

This article will document the ­infamous P0456 code — 0.20 leak detected. A small leak code can be the most challenging for any of us, so the following is a suggested plan of attack.
Through my research, I’ve found that all of the auto manufacturers appear to run their EVAP monitors in a certain sequence, and I have studied this in detail for GM, Ford and Chrysler vehicles. figure 1: p1495 and p1494 — check by the pcm at koeo and koer
We’ll begin our diagnostic journey with Chrysler. There is a manual that Chrysler produced some time ago that offers an engineering perspective into the operation of its Leak Detection Pump (LDP) system — Leak Detection Pump Operation and Diagnosis (Publication No. 81-170-00006). (It can be purchased off of the Chrysler website if you’re interested in reviewing it, or you can contact me at figure 2: p1486 — blockage check per the pcm at koercarlton196100@yahoo.com and I will provide additional information on it.)figure 3: ldp pump mode sequence
Upon review of the manual, it shows that when the system is under test, it begins with a P1495 or P1496 check. This is a check to see if feed voltage applied (>10.4 volts) to the LDP has made its way back to the PCM to be grounded for pump operation. This is done at KOEO. figure 4: a forced evap monitor was run on our subject vehicle.
The second check is a P1494. This is done on startup and the LDP solenoid is energized to see if it’s able to operate on command. Note: Make sure that there is a good vacuum source to the pump so that false codes are not set. figure 5: p1495 and p1494 — check by the pcm at koeo and koer.
The third check, P1486, is a blockage test for the system. If the system passes this series of checks, the system has passed all electrical and mechanical testing for the system per the PCM.  figure 6: p1486 — blockage check per the pcm at koer and pump mode.
The series of waveforms in Figures 1 through 7 show the beginning portions of the test via a lab scope. figure 7: test mode shows less than 6 seconds —p0456 is set.The blue pattern is the LDP switch and the red pattern is the LDP solenoid. These serve as known-good patterns.

The next test in line is called “Pump Mode.” This is the time period for which the pump will be used to pressurize the system, and, per Chrysler, no codes will be set during this time period. Once the Pump Mode is complete, the system will then begin what is called “test mode” or “pump period.”
The EVAP system has now reached a point in its sequence where leaks can be tested. The size of the leak is based on when the purge solenoid stopped and how long the LDP switch remained in the open position. This time element was determined by Chrysler. Here are the time periods:
  — Less than 0.9 seconds equals a gross leak
  — Between 0.9 to 1.2 seconds equals a medium leak
  — Between 1.2 to 6 seconds equals a small leak

We now begin our story with a 2003 Dodge Caravan with a 3.3L engine. The EVAP system has set a code P0456 ­indicating that a small leak may be ­present. Note: It is always advisable to check for TSBs and any preliminary service information that may be available on the vehicle you are working on. This could save valuable diagnostic time.
A TSB check does indeed yield a bulletin: MIL Illumination, Erroneous DTC P0456 — EVAP Leak Monitor 0.020 Leak Detected. The fix per this bulletin is a new PCM. The PCM part number is not in the range indicated on this bulletin, so we will proceed with our diagnosis.
We start by forcing the monitor to run with a DRB III scan tool.
The activity is monitored with a lab scope to aid in the learning process. The following screens denote the process as witnessed:
A failure has now been confirmed; a code P0456 is stored in the controller’s memory.
A smoke test is done on the system and no smoke can be seen coming from the vehicle. We use a smoke machine with a flow meter to confirm the diagnosis. figure 8: this was a very ­difficult leak to find and isolate. the gas tank was dropped in an effort to ­isolate the leak.
The EVAP system is then isolated from the tank and retested, but the leak is not present.
Next, we test the fuel tank as a standalone unit. See Figures 8 and 9.
The leak has been found! Figure 9: The leak has been found!
A less-than-impressive repair to the gas tank was the cause of our leak. This Pulling Code case is now closed. 

The following two tabs change content below.

Carlton Banks

Technical Contributor for TechShop, Carlton is an emissions trainer for three Midwest states. He's made it a mission to find the truth in emissions-related codes.
Latest articles from our other sites:

Leveraging SWOT Analysis

As I teach all of my clients, effectively improving an organization’s sales and customer service effort should begin with an honest evaluation of the company’s current performance to establish a baseline...More

Taking The Mystery Out Of Labor Inventory

Many colleagues in the industry seem to be confused about managing labor inventory in their shops.  Much of the confusion comes from the terminology thrown around the industry and because the definitions...More

Saab: Fuel Sending Unit Replacement

The 2006 Saab 9-3 Sport sedan came in on the hook and the tow truck driver said, “I think it needs a fuel pump.” The gas gauge was reading less than a quarter of a tank and the low fuel warning light...More

Lithium: An Element That Is Charging Ahead

What is an EMV? As you read the hybrid and plug-in articles that my company, ACDC, is writing this year, we have coined a new term: EMV (electric motor vehicle). Rather than use hybrid, plug-in hybrid,...More

Nivomat shocks can be found on a variety of vehicles. They are self-leveling shocks that use an internal pump on the piston to control the level of the vehicle. There are no external lines or connections. Five...More

PHOTO TECH: How a Brake Pad is Made

Even with zero moving parts, the common replacement brake pad is one of the most difficult to engineer and manufacture components on a vehicle. From the initial design to the final packaging, we...More

Top 5 Tools: Daniel Sjobeck, Roseville Auto Repair

Daniel Sjobeck, tech Roseville Auto Repair Roseville, MN A good toolbox. You can have the best of everything, but it’s no use if you cannot find it. Power Probe – One of the greatest ­inventions...More

GearWrench Expands 3/4” Ratchet Line

GearWrench has announced its new 36-inch long 3/4" Drive Knurled Chrome Ratchet Handle (SKU: 81403). Also announced was the availability of its 3/4" Drive Quick Release 24-Tooth Ratchet Head (SKU:...More