This month, we’ll be taking a look at the Honda line of cars with an eye toward some of the problems that have motivated owners to find their way to your shop. With the longevity these cars enjoy, it pays to take a look at some of the older models, as well as the more modern versions, to capitalize on service opportunities.
One of the common check engine light problems you’ll encounter on Hondas is a misfire code with no apparent misfire. Many times, this problem will be traced back to tight valve lash. Obviously, a tight valve will pass the audible test every time. But, it’s the tight valves that will set the check engine light in the best case, and if it’s ignored long enough you’ll be looking at a low-compression situation caused by a burnt valve.
This problem is more evident on certain models, with the CR-Vs built in the early 2000s being common enough to result in a TSB with Honda participating in some of the repairs in years past. These engines run a relatively tight lash with little room for error. While it’s most common on that model, we’ve seen it on others, so whenever we’re faced with a mysterious misfire code we check and adjust the lash. We recommend lash adjustment every 30,000 miles on the problem cars.
On the other four-cylinder cars, we make sure the lash is checked and adjusted with timing belt replacement, and we always adjust to the wide end of the spec. While not as common with the V-6 engine, there have also been some reports of tight valves on them. As you would expect, it’s a considerably larger job to adjust the valves on the six cylinders, so be sure you’re heading down the right path.
The key to the valve problem is the fact that the misfire will be most prevalent when the engine is cold and the valves are at their tightest. As the engine comes up to temp, the alloy head will expand at a greater rate than the valve moving the rocker away from the valve. If the misfire persists when the engine is warm, exhaust the other possibilities before charging into the lash adjustment.
Another less than obvious cause of the P030X series of misfire codes can be a leaking head gasket. While most common on the Civic line, this problem will usually offer some additional clues but one of the first may be a slight misfire on startup that will trigger the light. Like the tight valve, this misfire may be barely noticeable on a cold start and clear quickly as the engine temp increases. The difference being the head gasket leakage will always result in a loss of coolant.
Another common cause of P0300 codes in both the four and six cylinders is plugged EGR ports (this may or not be accompanied by an EGR code). The misfire is caused by excessive EGR flow to the cylinders that are not plugged. The EGR issue won’t show up until the engine is warm enough to command the EGR to function. This misfire will be evident only on light acceleration when the EGR is flowing. To pinpoint the diagnosis, simply unplug the EGR vacuum line or wire harness (if electronically controlled) and the misfire should be gone.
With the earlier four-cylinder cars, you can access the EGR ports by removing the core plugs in the intake manifold located near the mounting flange. To remove the plugs, carefully drill them in the center so they can be tapped for a bolt that will allow you to use a slide hammer for removal.
We try hard not to drill through the plugs to prevent introducing shavings into the intake and we usually find ourselves reusing the plugs, although replacements are available from the dealer. On the later-model four cylinders, the ports can be accessed without having to drill the plugs, but the injectors will have to be removed so the cover plate can be lifted to expose the offending ports.
Today, you will be seeing this EGR flow issue and the P0401 and P1491 codes more often on the six-cylinder equipped vehicles, with the more severe cases setting a misfire code. There is a TSB available (05-026) that covers the procedure for clearing the ports and outlines the installation of an upgrade kit that includes a new EGR valve as well as a pipe that is installed in the lower manifold. Honda performed many of these upgrades under an extended warranty, but we are still seeing quite a few that didn’t receive the upgrade.
We’ve had good success cleaning the ports on these cars and opening up the passage in the lower manifold where most of the blockage takes place. Remove the upper intake plenum to access the ports on the V-6 engines. It can be a bit more challenging getting the longer EGR ports clean, but it’s not a difficult job. Since the carbon has accumulated in the relatively cool intake manifold, it is usually soft enough to remove with stiff brushes and solvent. The TSB covers the procedure well.
While these problems will lead to misfire codes that can be difficult to pinpoint, don’t overlook the basics. The same long service intervals that lead to the tight valves also result in spark plugs with wide gaps that will increase the demand on the coil, or coils if the vehicle is equipped with coil on plugs. With many of the older Hondas still on the road, you will likely find yourself looking at a no-spark condition as these cars continue to accumulate mileage.
The coils as well as the igniters on these earlier cars have been known to fail, with the coils being more common lately. Perform an easy check by grabbing your tach and dwell meter and looking for a signal at the negative terminal of the coil. It should spark if it shows any dwell, and it goes without saying that while you’re under the distributor cap, it’s a good time to replace the cap and rotor with OE or OE-equivalent parts.
On the later mid-2000 vehicles where the crank angle sensor is mounted on the block below the water pump, coolant from a leaking water pump or spillage from a pump replacement can lead to bad connections at the sensor. This can result in poor run and stalling concerns and misfire codes. Be careful when doing water pumps on these cars. It’s easy to fill the connector cavity in the sensor with coolant when the pump is removed. There have been reports of ECUs being damaged by the short created by the coolant, which would certainly ruin a good timing belt job.
CAM AND CRANK SENSORS
The camshaft sensors have also caused some problems. While not very common, they should be considered when you’re faced with an intermittent no-start or stalling issue. They do seem to be affected by heat and will be a problem on the road, but operate fine when the vehicle comes off the truck at the shop. If you have a stored code for a cam sensor with a history of a stall, I would change the sensor. It’s not an expensive part and it doesn’t take long to install, so it’s better to be safe than sorry.
While we are talking about the cam and crank sensors, you should also keep in mind that if the sensors get out of phase due to the cam belt or timing chain jumping a tooth, or a belt that was inadvertently installed out of time, the engine may try to start but won’t continue to run. This is often mistaken for an immobilizer problem, and while a sensor code may be set at the same time, it’s just as likely for the code not to set.
ELECTRONIC THROTTLE CONTROL
While Honda is taking advantage of what drive-by-wire technology has to offer, and there have been few problems with this system, it hasn’t been trouble-free.
The P0506, P0507 and P0511 codes are related to idle control issues on both the drive-by-wire and the cable-controlled systems. The P0511 indicates a problem with the idle air control valve that is used on the mechanical systems up through 2005, while the P0506 and P0507 codes relate to idle speeds not expected on either system.
The most common complaint reported with the drive-by-wire systems involves the idle speed being higher than expected, followed by a stalling complaint often on the same car. As always, the first step is to check for codes — both temporary (pending) and hard codes should be considered. As I’ve said in previous articles, if your shop has yet to make the investment in an enhanced scanner, you should really consider it. The drive-by-wire system has numerous codes that are associated with this system that will get you moving in the proper direction.
Honda takes a different approach than other carmakers with its electronic throttle control. Looking at a 2006 Accord, a throttle cable is used to connect the pedal to an underhood accelerator pedal position (APP) sensor. As the name implies, this sensor tells the throttle actuator control module located behind the right-side kick panel where the pedal is, while the throttle position switches mounted on the throttle actuator report where the throttle plate is and how it’s reacting to commands.
If any of the components report a different-than-expected response, a code will be set that will steer you in the right direction for diagnosis. From all reports, most failures have led to throttle housing/actuator replacement. With the expense of these units, depending on the mileage, it may pay for the customer to contact Honda to see if any extended coverage or consideration is offered.
Based on our experience, our first thought will be to clean the throttle body when faced with such an issue. This experience was gained on the mechanical throttles where we would restore smooth operation and a solid idle with a thorough cleaning of the plate and housing to eliminate sticking, and restore the proper clearance between the plate and housing. When it comes to the electronically controlled throttles, things are a bit different. Cleaning the throttle plate and housing isn’t as important or successful now since the throttle plate can be commanded to open to compensate for any restriction of air flow that would have lowered the idle speed more than the IAC could compensate for.
But care must be taken when cleaning either throttle. With the mechanical throttle, be careful not to let the solvent and debris find its way down the bypass port that leads to the idle control valve; the consequences of that are obvious. On the electronic throttle, inspect it first and if it doesn’t really need to be cleaned it may be a better strategy to leave it alone. If it does need to be cleaned, use the solvent sparingly. Spray some solvent on the brush or rag and wipe the carbon, rather than spraying the solvent into the housing where it can find its way into the sensitive electronics. Also be sure to stay clear of the throttle plate if the ignition is turned on to prevent any damage to your fingers.
RELEARN PROCEDURES
There are relearn procedures for the throttle, crank and cam sensors as well as the ECU/PCM. Again, an enhanced scanner with Honda and Acura software makes the job as easy as pressing a button, but procedures are available in your service information that don’t require a scanner.
Rather than list them all here, we’ll look at the ECU/PCM idle relearn on a 2006 four-cylinder Accord as an example. Be sure all the electrical loads are off, clear the codes, reset the ECM/PCM, turn the ignition to the on position for two seconds, start the engine holding the speed at 3,000 rpm until the cooling fan starts or the coolant temp reaches 195 degrees, return to idle speed for five minutes with the throttle fully closed.
If the cooling fan runs, do not count that fan run time in the five mins. The learn/relearn procedure for the crank and cam sensor is similar with a road-test step (the procedures should be readily available in your service information). Like anything that is computer-controlled, follow the procedures closely and be sure you’ve cleared the memory before you start.
