K-light code 52, exhaust values ok

[Charlskalas]

Hi,
Long time lurker first time poster. I have recently acquired a Peugeot 306 cabriolet (2.0l, phase 1). 
According to the seller, the check engine light has been going on and off for as long as they had the car (10 years), but with no apparent problems when running. 

I read the error code as 52: Mixture control, supply voltage, air or exhaust leak. 

I am pretty sure that there are no problems with the exhaust, as the car just passed the annual state testing procedure (eq MOT) without any CO or lambda problems. 

The only real issue I have noticed is that the car hesitates to accelerate if pushed hard. However, I dont notice any issues when idle or when accelerating moderatly (although I dont know how the car should feel when 100%, so nothing to compare with unfortunately). 

Could it be the MAP-sensor acting up? Anyone know if this would fall under error 52, or if it could be something else?

[Mighty306]

Welcome to the club. Funnily enough the engine check light has just popped up on my 2.0l 16v XSi. Just stuck it on PP .....bl**dy mixture regulation code again. That error doesn't unfortunately point to any particular element in the system involved in managing air-fuel ratio, making for a difficult diagnosis. In the past I've had lazy lambda, faulty MAP & TPS and yet on each occasion PP only gave me a mixture regulation code, not one that pointed to the sensor causing the trouble. Assuming you can't narrow much down via OBD data, any of the following could be looked at/for as potential culprits (in no particular order):

> Intake vacuum leak (In the UK, unless it was a tiny leak the car would possibly fail on emissions, so assume it would be the same where you are)
> Poor spark
> Fuel delivery - fuel pressure (pump & pressure regulator). Also poss check EVAP valve isn't sticking open.
> Lambda / O2 or associated wiring (but you've discounted that on the basis the car just passed its test)
> MAP sensor or wiring to it
> Throttle position sensor or wiring to it (could be a slight dead spot causing the hesitation as throttle opened. This usually happens near idle position. The TPS is easy to test using a multimeter).
> Mechanical cause

....I know it's a long list (but not even exhaustive). In PP you can at least look at some live data and get a sense of the information the ECU is receiving.  If it's an intermittent sensor issue though, or it's only slightly out (but just enough to throw a light) then it can be hard to spot.


At the end of the day these aren't OBD2 compliant & you don't get a fraction of the diagnostic info you would from a modern car.  That leaves you following intuition to a degree. If I were you I'd start with the TPS, then look at the MAP. After that, take your pick. Good luck!

[Charlskalas]

Thank you! That is actually very helpful just to know that I am somewhat on the right track, will report back once I get to it. 

Never worked on Peugeots before, usually a SAAB guy (guess my home country), but the old SAABs are getting expensive even here.

[Martin306]

Okay so generally when you introduce air to an engine quickly, if there is hesitation the engine isn't getting enough fuel.

I would first check the vacuum reference going to the fuel pressure regulator from the inlet manifold, and check that the fuel pump is actually getting 12-13v when the engine is running and that the fuel rail is receiving the pressure indicated/marked on it.

It might be worthwhile changing the fuel filter as well.

A fault code like that isn't necessarily a faulty sensor, the ECU can only fuel trim so far and it assumes the sensor is faulty. the ECU cannot see mechanical problems such as low fuel pressure, so it would see a lean condition and flag a mixture issue because it cannot correct the values it is seeing on the lambda sensor.

Or if it's lean and you're using more throttle, it can sometimes show a MAP sensor failure, because it's not expecting to see a certain vacuum level for a given condition.

[Charlskalas]

I noticed something else while trying to fill up the tank today (for the first time). The nozzle shut off directly (several tries, different stations), although the tank should be half empty. I am suspecting the charcoal canister and will try to blow through it. I wouldn’t suspect the charcoal canister to cause the hesitant acceleration, but could it trigger the k-light?

[Mighty306]

I don't think the charcoal canister would cause the engine check light to come on because the EVAP system is pretty simple on these cars. The ECU controls the EVAP solonoid to allow an intake vacuum to draw vapours from the charcoal canister under certain conditions. The ECU knows whether it's open or closed & and that's it. There's no pressure sensor in the tank or anywhere else to give any indication that the system is leak free or that the canister is blocked.

EDIT: If the EVAP solonoid is stuck open there would be a constant vacuum sucking vapours in to the inlet manifold. That could cause a rick condition that the ECU couldn't make adjustments for. If removed from the car the operation of the solonoid is easy to check. Checking the ECU has control over it as it should is more of a challenge.

[Charlskalas]

After a bit of testing I am starting to think that it is the lambda after all.

Now, could anyone please point me in the right direction where to actually find this sensor?

I thought it would be accessable from the top, but perhaps it is a job from underneath. Haynes is of no help eitger unfortunately. It is a 8v 2.0 1995.

[Mighty306]

I'm afraid you've got to get right under the car. It's forward of the cat, wedged behind the front subframe! You can see if from the top but can't access it that way.

[Mighty306]

I'd forgotten your got an ph1 with the 8v engine but the lambda may still be in the same location. I can't check Servicebox until this evening I'm afraid.

[Charlskalas]

I'd forgotten your got an ph1 with the 8v engine but the lambda may still be in the same location. I can't check Servicebox until this evening I'm afraid.

Thank you, I think you might be right about that. Bugger that it isn’t as easy as the smaller engines where apparently it is the first thing you see in the engine compartment.

[Mighty306]

Looking back at your original post I'm reminded you said it passed its emissions test. If it was the lambda you'd have thought the emissions test would have picked it up, unless it's an intermittent wiring issue?

Have you checked the reference voltage on the main sensors with the ignition on btw?

Back to the lambda, I've checked Servicebox, and yes, it'll be where I said. It's because the engine is facing with the inlet towards the front and the exhaust facing back. I assume, like the 16v engine that the 8v engine is also canted back by a fair bit meaning access for exhaust components is really only possible from beneath the car.

[Charlskalas]

It’s true that a failing lambda probably should have caused a failed emissions test, but I have tested the other sensors and also checked the hoses for leaks so running out of possible causes. Because of the symptoms, and that the lambda sensor should be near its end of life anyways, I decided to give it a go. Only thing left would be to check the EVAP.  

Another thing I noticed was that the fuel filter seems to be of the wrong type, it is a Nissan branded fuel filter with both of the hose connections on top (looks like a diesel filter actually). I will change this as well, I guess it could be the culprit.

[Charlskalas]

Finally had the time and tools to change first the fuel filter (and all fuel hoses in the engine compartment, I understand that they should be ID 8mm but must have been replaced with 6mm hoses, causing the new original fuel filter to not fit the hoses). The new fuel filter did not fix the issue however, unsurprisingly. 

I then changed the lambda, and wow! Instantly, just driving out from the DIY shop, felt that the car was more eager to respond to the throttle, and the engine light has stayed off now for a few test rounds which would have triggered the light before. 

I have no idea how the car could have passed the emissions test, but goes to show that you shouldn’t really rule out the most obvious conclusion. According to the previous owner, the k-light had been on for 10 years, so perhaps the lambda had been replaced with a budget one somewhere along the line, I read somewhere that the car could be sensitive to non-original lambda sensors. I fitted a Bosch, which might not be original but working so far non the less.