My vehicle experienced the following Fault Messages:
- Reduced Braking Performance
- UpHill Assist Not Available
- TSA not available
- Downhill Assist Not Available
- ESC Not Available
- Power Steering Failure & Windscreen Wipers
Then today:
- Diesel heater symbol – which would not cancel. (Eventually RESET with powering down the car for 10 minutes).
On the Grenadier, the diesel pre‑heater / glow‑plug icon is not just about starting; it’s tied into the engine management, CAN‑bus, and voltage stability. When it stays on unexpectedly, it’s almost always a symptom of an electrical or communication dropout, not a genuine heater fault.
What the stuck diesel heater symbol tells us: The glow‑plug / diesel heater icon staying illuminated means the following:
The ECU didn’t complete its startup sequence: If voltage dips or a module doesn’t initialise, the ECU keeps the heater cycle “open” because it thinks the engine is still in pre‑start conditions.
CAN‑bus messages between the engine ECU and body control module were interrupted. When the CAN‑bus drops out, the ECU can’t confirm the heater cycle has ended, so the symbol stays on.
This is the same network that carries:
- ESC
- Uphill/Downhill Assist
- Trailer Stability Assist
- Brake system messages
- Power steering control
- Wiper control
This is classic Grenadier CAN‑bus instability, almost always triggered by low voltage or a poor connection.
Most likely root cause (in order of probability) on Early Build Grenadiers :
1. Loose or under‑torqued earth strap (very common on sub‑1500 builds). The main chassis earth strap on early Grenadiers was often not torqued correctly at the factory. A poor earth = unstable voltage = CAN‑bus chaos.
2. Battery quality issues on early builds. The first batches had batteries that were:
- Slightly undersized
- Prone to voltage sag in cold weather
- Sensitive to short‑trip use
A momentary voltage dip during ECU wake‑up can trigger every single warning you saw. The diesel heater symbol staying on is a classic sign the ECU didn’t complete its startup handshake.
3. ABS/ESC module moisture vulnerability
Early builds had a connector seal that wasn’t perfect. Moisture or condensation can cause intermittent CAN‑bus dropouts. When the ABS/ESC module drops off the network, you lose:
- ESC
- Hill assist
- Trailer stability
- Downhill assist
- Brake system messaging
4. Steering angle sensor dropout. Another early‑build quirk. If the steering angle sensor loses communication, the vehicle throws:
- ESC unavailable
- Hill assist unavailable
- Reduced braking performance
But this alone wouldn’t explain the wipers or diesel heater symbol — so it’s likely part of the picture, not the whole thing.
My combination of faults — especially the power steering failure, wipers activating, and diesel heater symbol stuck on — is almost certainly. My symptom list is a textbook match for an earth strap problem.
- A voltage or grounding issue causing CAN‑bus instability.
- And early build vehicles is right in the range where this is known to happen.
Is it safe to drive?
If the faults clear after a restart and the steering returns, it’s usually safe for short distances. But if:
- Power steering cuts out while moving
- Wipers activate randomly
- Diesel heater symbol stays on
…then the CAN‑bus is unstable, and that can become unsafe.
What a dealer will do for early build vehicles. They will almost certainly:
- Check and re‑torque the earth strap
- Update ECU and BCM software (several patches exist for early builds)
- Test the battery under load
- Check alternator output
- Inspect ABS/ESC module connectors
- Scan for CAN‑bus communication errors
Where to Check First (in order of likelihood)
| Check | Location | Why It Matters |
|---|---|---|
| Chassis earth strap | Passenger‑side chassis rail, behind front wheel | #1 cause of early‑build electrical chaos |
| Battery terminals | Under bonnet | Loose clamps = instant CAN‑bus dropout |
| Battery health | Under Rear Seat | Weak battery = diesel heater symbol + warnings Engine off: should be 12.6V+ Engine running: 13.8–14.6V (alternator charging) |
| Alternator output | Engine bay | Low charge = power steering + wiper faults |
| ABS/ESC connector | Near front axle | Moisture = braking/ESC warnings |
Grenadier Early‑Build Fault Table
| Symptom / Warning | Likely Cause | Why It Happens | Priority Check |
|---|---|---|---|
| Reduced Braking Performance | CAN‑bus dropout / ABS module | ABS module loses communication, so braking assist is disabled | ABS connector, earth strap |
| Uphill Assist Not Available | CAN‑bus dropout | Hill‑hold relies on ABS + ESC data | Earth strap, battery voltage |
| Downhill Assist Not Available | CAN‑bus dropout | Same as above — module offline | Earth strap, ABS connector |
| Trailer Stability Assist Not Available | CAN‑bus dropout | TSA uses ESC + yaw sensors | Earth strap, battery |
| ESC Not Available | ABS/ESC module losing comms | ESC is the first system to drop when voltage dips | Earth strap, battery, alternator |
| Power Steering Failure | Voltage drop / CAN‑bus loss | Steering ECU drops offline when voltage unstable | Battery, alternator, earth strap |
| Wipers activating randomly | BCM losing communication | Classic sign of CAN‑bus instability | Earth strap, BCM connector |
| Diesel heater symbol stuck on | ECU startup sequence incomplete | Voltage dip prevents glow‑plug cycle from closing | Battery, alternator |
| All faults clear after restart | Voltage / grounding issue | ECUs reboot cleanly once voltage stabilises | Confirms electrical root cause |
Grenadier Early‑Build Vehicles – Known Weak Points
| Component | Issue on Early Builds | Effect |
|---|---|---|
| Chassis earth strap | Under‑torqued, painted contact surface | CAN‑bus instability, random faults |
| Battery (factory‑fitted) | Marginal capacity, voltage sag | Startup faults, heater symbol stuck |
| ABS/ESC module connector | Moisture vulnerability | ESC, hill assist, braking warnings |
| Steering angle sensor | Occasional dropout | ESC unavailable, hill assist faults |
| Alternator | Intermittent low output on some units | Power steering + wiper behaviour |
┌──────────────────────────────┐
│ 1. Voltage Dip Occurs │
│ (weak battery, loose earth, │
│ alternator drop, moisture) │
└──────────────┬───────────────┘
│
▼
┌──────────────────────────────┐
│ 2. CAN‑Bus Instability Begins │
│ (modules stop communicating) │
└──────────────┬───────────────┘
│
▼
┌─────────────────────────────────────────────────┐
│ 3. Critical ECUs Drop Offline Intermittently │
│ • ABS/ESC module │
│ • Steering control module │
│ • Body control module (BCM) │
│ • Engine ECU handshake incomplete │
└──────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────┐
│ 4. Systems Dependent on ABS/ESC Fail │
│ • ESC Not Available │
│ • Uphill Assist Not Available │
│ • Downhill Assist Not Available │
│ • Trailer Stability Assist Not Available │
│ • Reduced Braking Performance │
└──────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────┐
│ 5. BCM Glitches Cause Secondary Symptoms │
│ • Wipers activate randomly │
│ • Power steering cuts out │
│ • Warning lights flicker │
└──────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────┐
│ 6. Engine ECU Startup Sequence Fails │
│ • Diesel heater / glow‑plug symbol stays on │
│ • ECU thinks pre‑heat cycle never completed │
└──────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────┐
│ 7. Vehicle Throws Multiple Fault Messages │
│ (appearing unrelated, but all caused by │
│ the same voltage/CAN‑bus event) │
└──────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────┐
│ 8. Power Down / Restart │
│ • Voltage stabilises │
│ • Modules reboot cleanly │
│ • All faults disappear temporarily │
└─────────────────────────────────────────────────┘
