HI there,
Recently my check engine light was continually flashing.
The car drives relatively fine, and my untrained ear doesn’t notice anything out of the ordinary.
I checked the codes today and the Scanner displayed : PO 300, 1141, 106.
Strangely, the check engine light (CEL) stopped flashing after I scanned the codes (wierd).
Its a 2000 mazda protege 1.6L , 243 000km.
Just installed a new timing belt.
What should I look at next?
Clean the cat with cat cleaner?
Put in new spark plugs?
If the problem started after you changed the timing belt, look no further. Do not drive a car with a flashing CEL or severe engine damage could happen even if the codes are gone for now.
Actually the problem started about three weeks after I change the timing belt
The 1141 downstream 02 sensor code has been there the longest…I am suspecting that could be triggering the other codes?
The p0300 is for misfires occurring on all cylinders (as opposed to only one cylinder). That’s likely what’s causing the CEL to flash, it running the engine w/that problem can damage the cat. The p1141 is for a problem with the heater circuit for the rear (after the cat) o2 sensor. And the p0106 indicates a problem with the MAP sensor.
The way a misfire is detected is the computer notices the crankshaft doesn’t accelerate like it should after a cylinder should be firing. So you’d be noticing that, unless it is only occurring on a low % of the firings. In other words you may have a misfire happening among all the cylinders, but only 2 or 3% of the firings. Given that, I’d say the main problem is the MAP sensor isn’t doing it thing correctly, or it isn’t connected to the ECM for some reason, or there’s an ECM fault. The MAP sensor is a primary input to the calculation which determines how much fuel to inject for a given engine load, so if not enough or too much fuel is injected, that will cause a misfire. Here’s a few things to try to get started
Before you do anything else . . .
Perform a compression test, wet and dry
Please post the numbers
What about cleaning the 02 sensors?
What do you mean by measure fuel trims?
Don’t bother. If cleaning works at all, it won’t work long.
A scan tool having “mode 6” capability is usually able to measure what’s called the “fuel trim”. When the engine is warmed up the computer relies mostly on the O2 sensor to set the fuel/air mixture. But it always compares how much fuel it is injecting based only on the O2 sensor compared to how much it would be injecting if it ignored the O2 sensor & used the throttle position sensor, MAP sensor, ECT sensor, etc. Ideally it would calculate the same amount either way, but in general there’s some difference between those two calculations. Caused by sensor problems, air/exhaust leaks, and rapid changes in engine load that the O2 sensor isn’t able to keep up with. If the fuel trim is +20%, that means the engine computer is injecting 20% more fuel based on its O2 sensor reading than it would have if it only used the other sensors. Likewise a -20% fuel trim means it is injecting 20% less (based on the O2 sensor) than the other sensors are telling it to. A good long term fuel trim is under 5%. Anything approaching 20% indicates a problem. How much the fuel trim is, and whether it is positive or negative provides a clue what’s wrong.
I forgot to mention that the car drives ok (CEL flashing somehow turned to solid) it only shudders when taking off from a standstill.
What does this suggest?
Shuddering most noticed when first accelerating from a stop is often caused by misfires, often due to a lean condition.
UPDATE: Took the car to my old shop teacher…he tried to do readings with his scanner…but there was no fuel trim function.
He did run a test on the downstream 02 and that was giving low readings, indicating that it was running on the rich side, so he was adamant that it wasnt a vacuum leak issue.
He was very confident that it was spark plugs and told me to change them, which I did, heres are some pics tell me what you think about them? They were drenched in oil when I took them out, which another mechanic friend says is due to the leaking valve gasket.
Im going to reset the code and see what codes come up…
“ask your shop to test the resistance in the heater circuit. if that’s no good, replace the rear O2 sensor.”
I have a multimeter…how do i test this?
If the gap is within spec, I wouldn’t say the plugs are the cause of the problem. (From the 2nd photo, the gap does look a on the wide side, suggest to use a set of feeler gauges to measure it.) I’ve never seen a gold color appear like that on the outer electrode (the curved one). On my car’s plugs, when they come out after 20-30K miles, they look uniformly gray. But you may be using a different type of plug.
You’ll need some sort of repair manual which has wiring diagrams for you car. Or maybe you can find the circuit on the internet. Your O2 sensor is heated. The reason for this is so it starts working sooner after you start the engine. For reduced emissions. O2 sensors don’t produce a usable output until they are quite hot. There will be a 2-wire (or possibly 1-wire, and chassis ground) connection to the O2 sensor for the heater. It’s just a resistance heater (works like a toaster), so to check if the heating element has burned out or not, you’ll have to measure the resistance of that resistor by connecting your meter to the two wires going to the heater (after disconnecting the sensor from the wiring harness). Generally will measure in the 5-30 ohms range. If it is burned out, infinity.
Suggest to not go into parts replacing mode until your shop has verified the MAP sensor is working correctly, and you have a set of fuel trim measurements in hand. Any shop having the Mazda scan tool can provide you the fuel trim data.
As I mentioned the valve gasket is leaking.
the car already has 242km so I have to be wary of how much $$ I invest in it.
The body has considerable amount of rust, and I no clue how the struts and suspension is.
My policy is, any repair over $100…not worth it on a car that is barely worth $800 ( I already invested nearly $3000 in repairs since 2014 - in canadian dollars).
Our objective is for the car to run well for the next two years
Thanks George.
As an aside: why do we have to buy new plugs? As opposed to just cleaning them up with a wire brush?
I sure in poor third world countries, where owners appreciate their cars more, (such as cuba - thats what they do)
Do you think the leaking valve cover gasket could be the cause of some of the problems? ie leaking oil into exhaust, oil on plugs, boots,
Its quite a dirty engine.
Cuba has old cars running because of political embargo’s and no a wire brush is not the answer.
