We recently had a late-model Sentra towed in with a no-crank complaint. This was the first time we were faced with a smart-key-equipped Nissan that did nothing when the start button was pushed. My first step on any diagnosis is to put the enhanced scanner on the vehicle and perform a full scan; I use the time required for the scan to get into the service info and get familiar with the system. By looking at the wiring diagram, you should be able to get a good idea of how the system works. In the case of our Sentra, we had no codes, but by looking at the body control unit data we were able to see that the brake switch wasn’t changing status when the pedal was depressed. A quick look at the brake lights confirmed the stoplight switch was working, and a glance under the dash revealed there was a separate switch for the starting system that was the problem.
Another best practice that applies to servicing both the Altima as well as the Sentra is to be careful when cleaning the electronic throttle body. When Nissan went to electronic throttles, it was common to end up with a high idle after the service was done, particularly if the unit was flooded with cleaner. Now we are careful to use the cleaner on a rag to wipe the unit clean.
If you end up with a high idle and a P0507, for instance, you will need your enhanced scanner to do a throttle relearn. Before starting the process, be sure the conditions are met as listed on the tool. Some of these can be stubborn — more so if the idle is very high and in the 2,000 rpm range. It may be necessary to remove a spark plug wire to get the idle down, but this will set a misfire code. The engine shouldn’t be run longer than it has to ensure no damage is done to the cat converter.
A tip that I’ve used with good results is to have the engine running with your scanner hooked up. With the engine idling, unplug the air mass meter and plug it back in. With the engine still running clear, check the mass air code and see if the idle doesn’t return to normal. I don’t know why this works, but it has gotten me out of jams when I couldn’t get the relearn done otherwise.
A common problem you’ll see with Altima models is a P0335 code that represents a problem in the crankshaft position sensor circuit, sometimes accompanied with a P0755 engine speed code. This problem was identified early in its production, with Nissan issuing a recall that involved replacing both the cam and crank sensor.
Our shop got in the habit of changing both sensors whenever the code was encountered, but we have since changed our strategy to replacing only the crank sensor when that code is evident. The sensor is located on the firewall side of the engine and, while not easy to reach, presents little challenge when installing. There is one important thing to keep in mind during installation, and that is to be sure to plug the harness onto the sensor before installation, as it can’t be done afterward without modifying the connector.
And, like any code issue, keep in mind that the code is not part-specific, so be sure to take a look at the connector and wiring while you’re servicing this aspect of the car. Crank sensors have led to intermittent stalling, no-starts and long-crank complaints. If you are faced with any of these complaints and a P0355 code is stored, the sensor should be replaced.
The Six Cylinders
The six-cylinder-powered Maxima, Quest and Nissan pickups will have us seeing some of the same issues with the cam and crank sensors as their four-cylinder counterparts, but keep in mind that these sensors are looking at the relationship between the crank and cams. On the earlier twin-cam Maximas, the most common failure was with the ignition coils. If you’re lucky, you’ll get a solid misfire and code, but, more often than not, you’ll be faced with a P1320 “Ignition Control Signal Circuit Malfunction” code that isn’t cylinder-specific, but indicates a coil failure. At this point, you and the customer have a decision to make. Many times, the customer doesn’t have a driveability complaint, and it can be a hard sell to convince them to replace all six coils. Oftentimes, our customers choose to continue to drive the car until the cylinder in question throws a misfire code rather than replace all six coils as Nissan recommends.
While we don’t see the amount of coil failures we used to, it seems that the P0171 system lean code is more prevalent than it was in the past. A simple code to understand, the ECU sets this code when the system has to add more fuel than expected to maintain the desired air/fuel level.
Our first step when looking at one of these is to check the freeze-frame data on the scanner to see the conditions when the code was set. If it’s lean at idle, we’ll be looking for unmetered air finding its way into the engine (a vacuum leak); if the code was set at highway speeds, we would be thinking fuel delivery would be the likely issue.
When we talk about fuel delivery today, it includes everything from the fuel pump, filters and pressure regulator, as well as air mass sensor, air/fuel ratio sensors, temp sensors and injectors. If you should get a lean code for one bank, your first check should be to look at the fuel trim numbers for the other bank to see if it’s also lean.
Short-term trim will tell us what’s happening now, while the long-term number tells us what has been happening in the past and what the ECU has done to compensate. We are looking for numbers near zero when looking at generic OBD data. If you see long-term in positive 20 range with short-term right near it, you know it’s lean even if it hasn’t set a code for that bank yet. Armed with this information, you can now look at what will have the engine running lean, without concentrating on just one bank.
If freeze frame has you looking for a problem at idle speed, there are a couple of spots to concentrate on after you’re sure that the air/fuel ratio, oxygen sensors and other sensors are working as they should. Take a few minutes looking at live data: Are the temp sensors reporting as expected? Are all the exhaust sensors responding as you would expect to throttle input? Look at the manifold vacuum and short-term trim; if the vacuum is good at idle with short-term near zero, the problem may be intermittent.
It is worth noting that with many makes the long-term trim is returned to zero when codes are cleared. That is not the case with Nissans. In order to clear the trim memory, you have to use the memory reset option on an enhanced scanner or disconnect the power supply to the ECU.
If the car is in the shop with low manifold vacuum and high short-term trims, look for unmetered air finding its way in. Being old school, I’ll usually start with my stethoscope listening for leaks at cracked or soft hoses. I’ll also check that all the air intake ducting and hoses are intact and secure so all the air is passing through the air mass sensor. Hidden vacuum leaks can be detected at the evap purge valve or EGR system. If the EGR is leaking, it will be warm to the touch.
As much as I value my stethoscope, I’m willing to admit that smoking the intake is the more efficient method of detection. If you find yourself tracking down a leak on a Quest, be aware that there is a vacuum reservoir mounted on the intake manifold equipped with a one-way valve. This device will not see the smoke introduced in the manifold. With some reports of these devices leaking, be sure to take the time to check it.
If the system lean code was set at higher speed and rpm and there is no report of lackluster power, a bad mass air meter, intake plumbing or exhaust sensor could be the culprit. I make sure the air intake is intact before heading out on the road test.
Next, I bring up the PIDs that I want to look at while on the road. In this case, I will be looking at calculated load, coolant and intake air temp sensor, and short- and long-term trims on both banks. This will give us a good overall look at fuel delivery to the cylinders. I like to use calculated load to look at the air mass sensor — if you can get to near 100 on calc load on a wide-open throttle uphill pull, it’s a safe bet the sensor is doing its job.
If you can’t do better than 60, it’s time to look closely at the sensor. If cleaning improves the number, you know you’re on the right track. You can get a good indication of how the exhaust sensors are working by watching the trim numbers. If the short term is quickly responding to the inputs of the driver, it’s safe to assume they are reporting as expected and not causing the problem.
You’ve probably noticed that I haven’t mentioned fuel pressure or volume testing. If we were dealing with a power complaint and seeing a lean code, the pressure volume test would have been one of the first tests I would’ve performed. However, while I’ve seen fuel pump failures on Nissans, I have never experienced a pump causing a lean code.
The same can be said for exhaust leaks tricking the O2 sensors into thinking the engine is lean. I would address any exhaust leaks before going too deep into the diagnostic process, but experience tells me that if we have a recurring lean code, we should be concentrating on the previously discussed items.
I’ll leave you with a Nissan story that happened just recently: The phone rings and it’s one of our better clients letting us know that his 2002 Frontier just stopped running and is getting towed in. Whenever we get a car on the hook, I like to do a quick triage to find out what we are facing so that parts can be sourced and we can let the customer know when they’ll be back on the road. While we usually have a more experienced tech take care of it, when time permits, I like to let the newer techs take a look to get experience. This was one of those times.
This Frontier used the single-cam version of the V6 with a distributer, and our tech’s first thought was the fuel pump or maybe even the pump bracket was off since we’ve seen weather take its toll on that wiring in the past. As a quick check, he introduced a little fuel into the manifold to see if the truck would start and die. In this case, the truck just cranked with no attempt to start. The next step was to check for spark, where he found none coming out of the cap.
Moving along, since this model had an internal coil, the distributor cap was removed in order to check for spark at the coil. With the cap removed, it was noted the rotor was in tough shape and there was some movement in the shaft in the upper part of the distributer shaft. It was also noted that it was a rebuilt distributer, which isn’t unusual on older cars since it was serviced as a unit and there had been some problems with position sensors.
With the spark tester hooked to the coil tower, there was no spark, but now our tech knew why — the distributor wasn’t turning. Taking a few bolts out of the timing cover allowed him to confirm that the timing belt teeth were stripped off at the crank pulley. His first question was, “Why didn’t it spin effortlessly like the other broken belt jobs I’ve done?” But rather than just answer him, we engaged in a discussion, and he realized that since the cams were still in-time, the pistons were pushing against some compression. Armed with the knowledge of a bad belt, it did sound like it was spinning pretty easily. Luckily for the customer, these engines are freewheeling, and it suffered no internal damage. We were able to tighten the screw in the distributer to eliminate the play in the rotor.