Land Rover Repair: Misfire & rough running, solenoid valve, engine coolant temperature

Question
I recently purchased my 03 Discovery II. It had a minor stumble during the test drive but I figured plugs & wires but later discovered they are new.  Since then it has gotten worse and is the worst when fully warmed up & the codes said something about the secondary air injection.  I have heard something about an electrical conection under the passenger seat that causes problems.  Any enlightenment?

Answer
Hi Chris,

I'm not familiar with the electical fault you describe.  As for the SAI (Secondary air injection) causing misfires and rough idle, you should know that SAI is a means of reducing emissions during the initial start (cold starts):

"The engine control module (ECM) checks the engine coolant temperature when the engine is started, and if it is below 60º C (131F), the SAI pump is started. Secondary air injection will remain operational for a period controlled by the ECM (76 seconds for NAS vehicles, 64 seconds for EU-3 vehicles). The SAI pump operation can be cut short due to excessive engine speed or load."

Here are the codes usually associated with SAI:

P-code Description
P1412 SAI system fault (LH side) - air delivery not reaching catalysts
P1414 SAI system fault (LH side) - air delivery not reaching catalysts
P1413 SAI system fault (LH side) - air delivery not reaching catalysts
P1415 SAI system fault (RH side) - air delivery not reaching catalysts
P1417 SAI system fault (RH side) - air delivery not reaching catalysts
P1416 SAI system fault (RH side) - air delivery not reaching catalysts
P0418 Secondary air injection pump powerstage fault (e.g. - SAI pump relay fault / SAI pump or relay not connected / open circuit / harness damage).
P0413 SAI vacuum solenoid valve not connected, open circuit
P0414 SAI vacuum solenoid valve short circuit to ground
P0412 SAI vacuum solenoid valve powerstage fault - harness damage, short circuit to battery supply voltage

Could it be sensor failure?  Best to have the Disco diagnosed with a Testbook device and hope a fault is detected quickly.  You should return to the dealer and have them do this diagnosis while you still have warranty (of sorts).  This could be a very expensive repair if it turns out to be MAF (Mass air flow) related.

Since it is a recent purchase, you are within your rights to ask for service from the dealer who sold it to you.  Even private sales are usually included in such purchases.

Best of luck,

JohnMc