Hi All,

New User - Long Time spanner wielder

Disco 2 TD5 ES Premium Auto - Circa 159000 miles:
Historically, I've always had issues with M+S lights coming on, so i took the plunge, and have replaced the XYZ with an original beige reconditioned model. This solved my M+S issue, but after a few weeks of happy driving, I now have random bouts of EML/M+S, resulting in Limp Mode, no power at all, and no revs (but idles happily at 1000rpm)

It idles and revs absolutely fine (when stationary) but when you try to drive (which is kind of the reason I own the vehicle) I may manage 5 miles, sometimes I may only manage 5 yards. If I turn off and restart the engine, I can drive as usual, until it gets upset again...

So far, I have:
Unplugged and cleaned the MAF, cleaned a small amount of oil out of the Red and Black Plugs on ECU and the ECU connectors, changed the injector loom, drained and refilled gearbox, cleaned the throttle pedal plug and connector. But the issue persists!

Errors on the Nanocom read as follows:
Engine;
2, 8 - Ambient Pressure
4, 3 - Coolant Temp
6, 3 - Coolant Temp
6, 8 - Ambient Pressure
21, 6 - Driver Demand
24, 7 - Auto Gearbox

Gearbox:
P1884 - Can Bus error

I appreciate if youve read this far, I'm now think my possibilities are: Faulty ECU (but been perfect until recently - no water ingress etc), Bad Ground to ECU, potentially - faulty XYZ switch?

Your thoughts please and thanks

 

I’d lean to battery health and/or ground issues. Check not only the battery terminals and battery itself, but also follow the ground strap to it’s mounting point and ensure it’s clean and has a strong connection.

 

Ok, good news.

I went over the entire ECU pins and plugs again with an airline, a pick (for the female connectors) and more contact cleaner...

I also went through a comprehensive check list of what values the main sensors should be logging, and I realised the Ambient Pressure Sensor was only shows 2.46 kPa, rather than ~100kPa... It turns out the clip wasn't fully engaged on the plug, so it was making, sometimes, but not making most of the time.

Anyway, having done that, and recleaned the ECU, and checked all the earths, I went for a drive, and NOT ONE FAULT! Nothing logged in the Nanocom :-)

Check list - for future reference:
Parameter : Normal Reading : Notes / Fault IndicatorsBattery Voltage 12.5V+ (off), 13.8–14.5V (running) Below 12V off = weak battery. Below 13.5V running = alternator issue.Ambient Pressure (APS) ~100 kPa (ignition on, engine off) If far off (e.g. 80 or 120 kPa), APS sensor fault inside ECU.Manifold Pressure (MAP) ~100 kPa ignition off, up to ~230 kPa under boost Stuck values or >240 kPa = overboost/wastegate issue.Coolant Temp Cold ~ambient, rises smoothly to 85–95°C Erratic/jumping = loom/sensor fault. Stays cold = bad sensor.Intake Air Temp (IAT) Ambient to ~40°C under load Stuck high/low = sensor fault or wiring.Fuel Temp Ambient to ~70°C when hot Very high or implausible = wiring or sensor fault.Throttle Track 1 0.5–4.5V smooth rise Dropouts = loom/pedal fault.Throttle Track 2 Half of Track 1 (e.g. 0.25–2.25V) Mismatch triggers Driver Demand code.Throttle Track 3 Inverse/matching check Glitches = pedal fault.Injector Balance (cyl 1–5) -2 to +2 mg/stroke Large deviations indicate injector/wiring issues.Idle RPM 720 ± 20 rpm Fluctuation or unstable idle suggests fueling/air issues.Gearbox XYZ Position Matches lever (P–R–N–D) Mismatch = bad XYZ switch or wiring.