AUTO Veteran

The Motorist's Pride

500+
DIY Guides
75K
Community Members
1.2M+
Monthly Views

Interactive Diagrams

More Diagrams
Car Parts Odd One Out Quiz

Car Parts Odd One Out Quiz

A puzzle image presents a grid of automotive components: cover, fuel injector, air filter, turbo, EGR valve, fuel pump, intercooler, oil filter, glow plug, timing belt, spark plug, and piston. The challenge is to identify which component does not belong, testing your knowledge of engine parts and their classifications.

DIY Tutorials

All Tutorials
Troubleshooting

This Is Why Your Car Won’t Start Even With A New …

You fit a brand new battery, turn the key, and get nothing but a click or a silent dash. It's a uni…

3 months, 3 weeks ago
8 Mins read
Road Safety

Who is at Fault When a Car Turns Right and a Bike…

Have you ever wondered who is responsible for an accident when a car turns right and a bike goes st…

1 year ago
2 Mins read
Troubleshooting

This Is Why Your Car’s Door Won’t Latch Properly

A car door that won't latch properly is more than an annoyance. It's a safety hazard, a security ri…

3 months, 1 week ago
7 Mins read
Explainer

How a Car Engine Actually Works From Start to Fin…

Modern car engines are a symphony of controlled explosions. Every single time you turn the key, a p…

3 months, 4 weeks ago
9 Mins read
Startup Ideas

How to Start an Automotive Business With Almost N…

I hear it all the time. "I'd love to start my own shop, but I don't have the capital." It's the sin…

3 months, 3 weeks ago
7 Mins read
Explainer

The Benefits of Catalytic Converters in Vehicle E…

Catalytic converters reduce harmful emissions, improve fuel economy, and extend engine life. Signs …

1 year ago
4 Mins read
Explainer

People Left Concerned After Learning Why Some Hyb…

You park your hybrid in the garage, lock up for the night, and settle in. Then, from the silence, y…

3 months, 2 weeks ago
7 Mins read
Car Buying Tips

Why Engine Capacity Matters When Shopping For A N…

When it comes to purchasing a new car, one of the key factors that often dictates the price tag is …

1 year ago
3 Mins read

Forum Q&A

All Questions

Seeing a barometric pressure reading of 199 kPa on a 2011 Jaguar at ignition-on is a red flag, this value is physically impossible under normal atmospheric conditions.

Ramphele DL
Replies (2)

Ramphele DL : At sea level, you’re looking at roughly 100 to 102 kPa, and even at the bottom of the Dead Sea (the lowest point on Earth), it doesn’t exceed 108 kPa. So, 199 kPa suggests either a serious sensor input error or a corruption in the ECU’s interpretation of the signal. On Jags of this era, the ECU performs a barometric pressure snap shot during key on before engine start, using the MAP sensor as the measuring device since there’s no separate BARO sensor. If the intake manifold or MAP port is contaminated, restricted, or sees abnormal pressure (like a stuck open EGR or boost control issue), it can skew this reading.

Ramphele DL : But more commonly, it’s a circuit issue check the 5V reference line to the MAP sensor for voltage spikes or resistance. I’ve seen cases where a failing alternator or poor grounding introduced enough electrical noise to make the ECU think it was under 2x atmospheric pressure. Verify the actual supply voltage at the sensor with the connector plugged in (back-probing), and ensure the ground is solid less than 0.2 ohms to battery negative.

At sea level, you’re looking at roughly 100 to 102 kPa, and even at the bottom of the Dead Sea (the lowest point on Earth), it doesn’t exceed 108 kPa. So, 199 kPa suggests either a serious sensor input error or a corruption in the ECU’s interpretation of the signal. On Jags of this era, the ECU performs a barometric pressure snap shot during key on before engine start, using the MAP sensor as the measuring device since there’s no separate BARO sensor. If the intake manifold or MAP port is contaminated, restricted, or sees abnormal pressure (like a stuck open EGR or boost control issue), it can skew this reading.

Ramphele DL

Yes, a faulty O2 sensor can cause this issue. It helps regulate the air-fuel mixture. If it's not working properly in cold conditions, the engine may run too rich or lean, resulting in rough idling and vibrations.

Jimna Mustafa
Replies (3)

Alvin Knex : If it’s the O2 sensor, why would it only happen when the engine is cold? Wouldn’t it affect performance all the time?

Jimna Mustafa : Good observation! Many O2 sensors only become active once the engine reaches operating temperature. When cold, the engine runs in 'open, loop' mode and ignores the O2 sensor, relying on preset fuel maps. If the sensor is failing, it might only cause issues once it starts influencing the fuel mixture, or if it sends incorrect signals during warm-up.

Alvin Knex : Turns out the upstream O2 sensor was failing. Swapped it out, and the violent shaking is gone. Thanks for pointing me in the right direction!

If it’s the O2 sensor, why would it only happen when the engine is cold? Wouldn’t it affect performance all the time?

Alvin Knex
Replies (1)

Jimna Mustafa : Updates?