What to look for in knock sensor failure
First off there are few things that you need to consider when diagnosing and replacing a knock sensor on Toyota vehicles.
- Some Toyota models have two knock sensors(left bank and right bank)
- It’s not un-common to have knock sensor wire failure
- The knock sensors are usually priced at or above $100.00 each, even if purchased aftermarket.
- There are two types of sensor brands used on Toyota vehicles
Nippon Denso Knock Sensor
Matsushita Knock Sensor
So, there are some things to consider when replacing the knock sensor. Doesn’t matter if you perform this yourself or have a repair shop do the repair. These things should still be considered.
When replacing the knock sensors the upper and lower intake manifold has to be removed and that alone is a lot of work. If the vehicle has dual sensors (one on each bank) you may want to consider replacing both of them while the intake manifold is removed. There is also a knock sensor wire that is common to have problems due to the intense heat under the intake manifold. The wire is fairly inexpensive at a cost of around $50.00 from the dealer and I always recommend to replace it regardless. Usually the insulation is hard and cracked and if it’s ok at the time of removal, there is a good chance that it won’t be after it has been disturbed. At the least the connector breaks where it connects to the sensor.
Other things to consider during knock sensor replacement on your Toyota
Since we know that the intake manifolds need to be removed, what other items have to be serviced while the intake is removed?
- Valve cover gaskets
- At the mileage your vehicle is at when knock sensor failure usually occurs is around the same time you start seeing the valve cover gaskets starting to leak
- Spark plugs
- The same goes with the spark plugs, and if they’re not due yet they will be due soon. If you’re model year has ignition wires you may want to consider replacing them also.
- Coolant crossover hose
- Underneath the lower intake manifold there is a coolant crossover hose. Toyota does make very good hoses, but think about the amount of time before that intake will ever be removed again? Hopefully never, replace the crossover hose. It’s pretty inexpensive anyways.
- Coolant passage cover plate
- After removing the lower intake, if you look in the galley way there you will see a plate. That plate seals a coolant passage and eventually will start to leak. If not leaking yet you may start to see coolant tracking or corrosion build up. This just means that it is leaking, but not at this time. At first it will only leak under certain temperatures, due to expansion and contraction of metal at the different temperatures.
Know that all that has been covered, you may be thinking this all adds up to be an expensive repair. How important is this really? Well, I will explain to you what a knock sensor does, but before I do that you may want to know that depending on the state you live in a failed knock sensor will result in a failed DEQ slip. Depending on the model I have also seen them cause automatic transmissions to loose overdrive. The computer does not want to command overdrive when this sensor has failed. This has stumped me before, especially when you get a customer that already knows about the check engine lite. The customer is also well aware of the cost to repair this and says, “Don’t worry about the check engine lite, I’m only concerned about why my transmission doesn’t have overdrive”. If you have not run into this before it can stump you pretty good.
What does a knock sensor do?
Knock sensors prevent predetenation. Up to a point, more power can be produced in an engine by increasing spark advance. But too much advance causes pre-detonation. Pre-detonation is also called knock, detonation and spark knock, pinging or pinking. Once knock starts, performance decreases and there is a risk of serious engine damage. Knock gets its name because it causes vibrations and banging in the cylinder. Mild knock causes a “pinging” noise that sounds like marbles or small ball
bearings bouncing on a piece of metal. Severe knock sounds like someone banging on a door. Mild knock reduces power, wastes fuel and increases emissions. Severe knock can destroy internal engine parts including the pistons, connecting rods, exhaust valves, head gaskets and spark plugs. The knock sensor detects these situations and prevents them from happening. So you can see why it’s important, it can save the life of your engine.
What causes spark knock or detonation?
- Detonation occurs when the air-fuel mixture doesn’t burn smoothly or ignites too soon.
- Detonation can be caused by “hot spots” in the cylinder, such as carbon deposits or spark plugs that are too hot for the engine.
- Detonation also occurs from excessive combustion chamber temperatures.
- Last but not least detonation will occur if spark timing is advanced too far or low fuel octane.
Other things to consider if your thinking you still don’t need the knock sensor.
When a computer detects a failed knock sensor it will default the ignition timing back 5 degrees or more to prevent spark knock. This will result in loss of gas mileage and also rob your vehicle of power. Especially in today’s vehicles, ignition timing (and mechanical cam timing) is one of the most important factors as to how we get so much power out of such a small engine. So, if you’re thinking your not concerned about replacing the knock sensor because you don’t hear any type of detonation in your engine. The reason for this is the good old fail-safe mode of computer-controlled engines. You most likely won’t even be aware of the fail-safe mode until you get the problem fixed and now notice an increase in power and fuel economy!