Engine management light won't stay off

renegadefm

Recently bought a citreon c1. 2006 model. 
We only had it a month and engine management light came on, so took it to my mechanic, he reset it for me and said the cause was build up in the catalytic converter and all I need to do is drive the car harder to clear it.  So I did this for a while on and off but after about 2 weeks its came back on today. 
I rang him today to see if I need a new catalytic converter, but he said no point, its only build up from emissions over time. 
It doesnt help we only do short journeys and not long runs to clear it regularly enough. 
So what do I do just drive it round with the light on? 

AdrianC

Sounds like some chinese whispers. Diesel filters clog up on short journeys, petrol cats don't in the same way.

Having said that, constant short journeys don't do cars any good. How short?

renegadefm

AdrianC said:

Sounds like some chinese whispers. Diesel filters clog up on short journeys, petrol cats don't in the same way.

Having said that, constant short journeys don't do cars any good. How short?

Normally just a few miles either to work or shops and home again. Engine barely gets hot and its off again. I know this cause heater only just gets hot and we have reached destination. But I must admit I seen when he connected the car to the gadget and it said catalytic converter. But he said replacing it would be a wasted expence. So I guess I either keep getting it reset, or drive around with it on. 
The only thing I am worried about is if anything else crops up that the light needs to signify it would be already on. 
In an ideal world the car dashboard would tell you what the fault is without having to go to a mechanic and being charged for trivial things, so the owner could decide if its serious or trivial as to whether the car needs a trip to the garage. 

EdGasketTheSecond

P0420 code; happens a lot but cars still pass the MoT. Just turn the EML off before the MoT using a cheap OBD2 scan tool from Amazon or EBay. You can fix it by soldering a capacitor/resistor in the second oxygen sensor circuit if you want to permenantly fix it; google it.

Goudy

Modern cars usually have two Lambda (or commonly called O2) sensors in the exhaust. (V6's and V8's often have four sensor, two per bank)

One before/pre catalytic convertor, this generates a signal via the heat in the exhaust gas temp and it's signal is used to adjust the fueling.

Hot gas, larger signal = lean engine so the ECU adds fuel.

Cooler gas, smaller signal = rich engine so the ECU removes fuel.

The second is behind/post catalytic convertor, this one isn't used to adjust the fueling, it monitors the performance of the catalytic convertor. It's part of the regs for modern cars to check/monitor/warn if there's a suspected problem with emissions equipment.

It sounds like that rear sensor is giving a reading outside it's perimeters, as you haven't complained of any running/driving issues I would guess there's a problem with the sensor or it's wiring rather than the cat. It's a common complaint of a lot of Citroen owners and owners of cars of a certain age tend get advised to ignore it and just clear the code prior to an MOT with a cheap OBD dongle and an App on a smartphone (called Torque Pro).

It you want it fit a new sensor, one can be had for around £70, but I'd want to be sure it was that, which means you really need the code from the ECU.

renegadefm

Thanks guys. No running difficulties at all. My mechanic just said I got to drive it harder, use lower gears more often. And dont use cheap supermarket fuel he said. 

Nuggy96

get some redex engine cleaner, give it a ferrari tune up by blasting it on motorway for around 20-30miles had the same problem with my corsa where my EGR valve blocked up

EdGasketTheSecond

Driving it hard is unlikely to resolve this. The cat does become less efficient and on a 2006 model is not as good as it was when new. You can't reverse that but as long as it passes the MoT check then you can just turn the EML off or as I said, fix it with some cheap components attached to the secondary lambda circuit.

Goudy

With a cheap OBD dongle and Torque Pro on your smartphone, you can pull the diagnostic code from the ECU and see if we're in the right ball park.

You can also log how both O2 sensors are performing, with this we could determine if they are both working correctly.

Driving it hard is a hope, as in hope that you generate enough heat in the cat to produce a signal within the ECU's perimeters, it's not really a fix, you'll just get the fault code back when it's detects the same fault again three times in the same drive cycle.

ElephantBoy57

renegadefm said:

Thanks guys. No running difficulties at all. My mechanic just said I got to drive it harder, use lower gears more often. And dont use cheap supermarket fuel he said.

I understand hard acceleration also creates more emissions that can result in clogging the DPF.

tonyh66

Check the wires to the pre cat sensor to see if they are damaged, had p0420 before and it was the wires touching the exhaust and burnt through.